Fix unhandled MANIFEST write errors

Summary:
The failure of WriteCurrentStateToManifest() was not handled properly.
If it failed, manifest_io_status was not updated, leading to
manifest_file_number_ being updated to the newly created manifest even
though its bad.

Test Plan:

Reviewers:

Subscribers:

Tasks:

Tags:

db/version_set.cc

@@ -5564,7 +5564,9 @@ Status VersionSet::ProcessManifestWrites(
         s = WriteCurrentStateToManifest(write_options, curr_state,
                                         wal_additions, descriptor_log_.get(),
                                         io_s);
-      } else {
+        assert(s == io_s);
+      }
+      if (!io_s.ok()) {
         manifest_io_status = io_s;
         s = io_s;
       }