Allow empty patch in git apply

[guineveresaenger]

Fixes #991.

Previously, #983 attempted to fix this behavior; however, the --allow-empty was erroneously appended to the git am command, not the git apply command, as it should have been.

Git documentation for git apply --allow-empty is the behavior we want.

[iwahbe]

Please confirm that this works as expected by manually testing make upstream upstream.rebase upstream.finalize before merging.

LGTM

[guineveresaenger]

Locally changed in pulumi-gcp:

apply() {
  assert_upstream
  assert_no_rebase_in_progress "$1"

  git submodule update --force --init
  # Iterating over the patches folder in sorted order,
  # apply the patch using a 3-way merge strategy. This mirrors the default behavior of 'git merge'
  cd upstream
  for patch in ../patches/*.patch; do
    if ! git apply --3way "$patch" --allow-empty; then
      cat <<EOF

make upstream

guin(master *) pulumi/pulumi-gcp🦉 make upstream     
scripts/upstream.sh "upstream" apply
Submodule path 'upstream': checked out '580cd0c10bc9d6334da3c248f4a3b0a897c8f57a'
Applied patch to 'google-beta/provider/provider.go' cleanly.
Applied patch to 'google-beta/services/sql/resource_sql_database_instance.go' cleanly.
[...]
warning: 3 lines add whitespace errors.
Applied patch to 'google-beta/services/storage/resource_storage_bucket.go' cleanly.
Applied patch to 'google-beta/tpgresource/labels.go' cleanly.

make upstream.rebase

guin(master *) pulumi/pulumi-gcp🦉 make upstream.rebase
scripts/upstream.sh "upstream.rebase" start_rebase
Submodule path 'upstream': checked out '580cd0c10bc9d6334da3c248f4a3b0a897c8f57a'
Rebasing in place at 580cd0c10bc9d6334da3c248f4a3b0a897c8f57a
Switched to and reset branch 'pulumi-patch'
Your branch is up to date with 'local'.
branch 'pulumi-patch' set up to track 'local'.
Applying ../patches/0001-Allow-disabling-the-partner-name.patch
[...]
Applying: fix label imports
Current branch pulumi-patch is up to date.

The full patch set has been cleanly applied to the './upstream' repository.
To "edit" the patch set, commit changes directly to './upstream'. When
you are done making changes, run:

    make upstream.finalize

to finish the rebase and commit those changes into the patch set.

make upstream.finalize

guin(master *%) pulumi/pulumi-gcp🦉 make upstream.finalize
scripts/upstream.sh "upstream.finalize" end_rebase
../patches/0001-Allow-disabling-the-partner-name.patch
../patches/0002-Add-nil-checks-for-sql-database-instance-flattening.patch
../patches/0003-rebase-bigquery_dataset.patch
../patches/0004-Add-flattening-of-self-managed-certificates.patch
../patches/0005-website-docs-d-tweaks.patch
../patches/0006-docs-patching.patch

../patches/0007-Exclude-scripts-dir-from-provider-go-module.patch
../patches/0008-Remove-duplicative-resource-token.patch
../patches/0009-Fix-794-with-an-unconditional-read.patch
../patches/0010-Remove-pattern-string-from-compute-forwarding-rules.patch
../patches/0011-fix-label-imports.patch
Submodule path 'upstream': checked out '580cd0c10bc9d6334da3c248f4a3b0a897c8f57a'
Applied patch to 'google-beta/provider/provider.go' cleanly.
[...]
Applied patch to 'google-beta/provider/provider.go' cleanly.
Applied patch to 'google-beta/services/sql/resource_sql_database_instance.go' cleanly.
../patches/0010-Remove-pattern-string-from-compute-forwarding-rules.patch:16: trailing whitespace.
  
../patches/0010-Remove-pattern-string-from-compute-forwarding-rules.patch:25: trailing whitespace.
  
../patches/0010-Remove-pattern-string-from-compute-forwarding-rules.patch:38: trailing whitespace.
  
Applied patch to 'website/docs/r/compute_forwarding_rule.html.markdown' cleanly.
Applied patch to 'website/docs/r/compute_global_forwarding_rule.html.markdown' cleanly.
warning: 3 lines add whitespace errors.
Applied patch to 'google-beta/services/storage/resource_storage_bucket.go' cleanly.
Applied patch to 'google-beta/tpgresource/labels.go' cleanly.
guin(master *) pulumi/pulumi-gcp🦉 git status
On branch master
Your branch is behind 'origin/master' by 4 commits, and can be fast-forwarded.
  (use "git pull" to update your local branch)

Changes not staged for commit:
  (use "git add <file>..." to update what will be committed)
  (use "git restore <file>..." to discard changes in working directory)
        modified:   patches/0001-Allow-disabling-the-partner-name.patch
        modified:   patches/0002-Add-nil-checks-for-sql-database-instance-flattening.patch
        modified:   patches/0006-docs-patching.patch
        modified:   patches/0008-Remove-duplicative-resource-token.patch
        modified:   patches/0009-Fix-794-with-an-unconditional-read.patch
        modified:   patches/0011-fix-label-imports.patch
        modified:   scripts/upstream.sh

no changes added to commit (use "git add" and/or "git commit -a")