When `super` is called at top-level with no arguments, `enclosingClass` is null, causing a segfault when trying to access its method name. This fix wraps the unnamed super call logic inside an else branch that only executes when `enclosingClass` is non-null, and adds a test case for the unnamed `super` call at top-level.
Add isInsideMethod helper that walks the compiler's parent chain to detect
if the current compilation scope is within a method. Use it in super_()
to emit a compile error when 'super' is used at top level or inside a
top-level function, with corresponding test cases for both scenarios.
Kyle Marek-Spartz
Bob Nystrom