fix(lint): useless assign with method call within a condition

fixes #468

spec/ameba/rule/lint/useless_assign_spec.cr

@@ -513,6 +513,33 @@ module Ameba::Rule::Lint
             CRYSTAL
         end
 
+        it "doesn't report if assignment is referenced within a method call" do
+          expect_no_issues subject, <<-CRYSTAL
+            if v = rand
+              puts(v = 1)
+            end
+            v
+            CRYSTAL
+
+          expect_no_issues subject, <<-CRYSTAL
+            puts v = 1 unless v = rand
+            v
+            CRYSTAL
+
+          expect_no_issues subject, <<-CRYSTAL
+            hash = {"foo" => "bar"}
+
+            def call(v)
+            end
+
+            unless v = hash["foo"]?
+              call v = "default"
+            end
+
+            v
+            CRYSTAL
+        end
+
         it "reports if assignment is useless in the branch" do
           expect_issue subject, <<-CRYSTAL
             def method(a)

src/ameba/ast/branch.cr

@@ -181,6 +181,8 @@ module Ameba::AST
         if loop?(node) && (block = node.block)
           on_branchable_start node, block.body
         end
+
+        true
       end
 
       def end_visit(node : Crystal::Call)