Fix edge case in findMethodInstanceContainer codeo

* Looks like we can have scenarios where 'self' for a closure
  executed in a module_eval context need not be the module
  but a different object. In that case, we still need to add
  the method to self => we need to get its metaclass first.

* This fixes crasher in this case:

-------------
require "minitest/autorun"

describe "A" do
  it "should do something" do
    def foo
    end
  end
end
-------------

Author: subbuss

core/src/main/java/org/jruby/ir/runtime/IRRuntimeHelpers.java

@@ -735,7 +735,14 @@ public static RubyModule findInstanceMethodContainer(ThreadContext context, Dyna
         for (DynamicScope ds = currDynScope; ds != null; ) {
             IRScopeType scopeType = ds.getStaticScope().getScopeType();
             switch (ds.getEvalType()) {
-                case MODULE_EVAL  : return (RubyModule) self;
+                // The most common use case here is where :
+                // - a method is defined inside a closure
+                //   that is nested inside a module_eval.
+                //   here self = the module
+                // - in the rare case where it is not (looks like it can
+                //   happen in some testing frameworks), we have to add
+                //   the method to self itself => its metaclass.
+                case MODULE_EVAL  : return self instanceof RubyModule ? (RubyModule) self : self.getMetaClass();
                 case INSTANCE_EVAL: return self.getSingletonClass();
                 case BINDING_EVAL : ds = ds.getParentScope(); break;
                 case NONE: