avoid SEGV in instance_eval without block.

instance_eval does not yield self.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@25988 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

vm_eval.c

@@ -1168,11 +1168,16 @@ yield_under(VALUE under, VALUE self, VALUE values)
 	block.self = self;
 	th->cfp->lfp[0] = GC_GUARDED_PTR(&block);
     }
-    cref = vm_cref_push(th, under, NOEX_PUBLIC, &block);
+    cref = vm_cref_push(th, under, NOEX_PUBLIC, blockptr);
     cref->flags |= NODE_FL_CREF_PUSHED_BY_EVAL;
 
     if (values == Qundef) {
+#if 0
+	/* The behavior of Ruby 1.8  */
 	return vm_yield_with_cref(th, 1, &self, cref);
+#else
+	return vm_yield_with_cref(th, 0, 0, cref);
+#endif
     }
     else {
 	return vm_yield_with_cref(th, RARRAY_LENINT(values), RARRAY_PTR(values), cref);