fix exception when completing between arglist and body

pkg/analysis_server/test/services/completion/optype_test.dart

Index: pkg/analysis_server/test/services/completion/optype_test.dart
diff --git a/pkg/analysis_server/test/services/completion/optype_test.dart b/pkg/analysis_server/test/services/completion/optype_test.dart
index 897fb20ded469b06bb253bd1d59c40dbee4ea2c8..b8dfadbbbdbb9a9413befad947f4a618b00a9e97 100644
--- a/pkg/analysis_server/test/services/completion/optype_test.dart
+++ b/pkg/analysis_server/test/services/completion/optype_test.dart
@@ -657,6 +657,12 @@ class OpTypeTest {
     assertOpType(typeNames: true);
   }
 
+  test_FunctionExpression() {
+    // BlockFunctionBody  FunctionExpression  FunctionDeclaration
+    addTestSource('main()^ { int b = 2; b++; b. }');
+    assertOpType();
+  }
+
   test_FunctionTypeAlias() {
     // SimpleIdentifier  FunctionTypeAlias  CompilationUnit
     addTestSource('typedef n^ ;');