Fix parsing function statements containing invalid tokens (#3838)

Fixes #3821.

JerryScript-DCO-1.0-Signed-off-by: Dániel Bátyai dbatyai@inf.u-szeged.hu

tests/jerry/regression-test-issue-3821.js

@@ -0,0 +1,35 @@
+// Copyright JS Foundation and other contributors, http://js.foundation
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+function check_syntax_error (script)
+{
+  try
+  {
+    eval (script);
+    assert (false);
+  }
+  catch (e)
+  {
+    assert (e instanceof SyntaxError);
+  }
+}
+
+check_syntax_error ('function')
+check_syntax_error ('function a')
+check_syntax_error ('function a"')
+check_syntax_error ('function a"b')
+check_syntax_error ('function a("b')
+check_syntax_error ('function a(b, "c')
+check_syntax_error ('function a(b, c"d')
+check_syntax_error ('function a(b, c)"d')