Fix instances where return value of mrb_method_search_vm is unchecked

Reported by @charliesome

test/t/nomethoderror.rb

@@ -20,3 +20,34 @@ assert('NoMethodError#args', '15.2.32.2.1') do
     end
   end
 end
+
+assert('Can still raise when BasicObject#method_missing is removed') do
+  assert_raise(TypeError) do
+    begin
+      BasicObject.alias_method(:old_method_missing, :method_missing)
+      BasicObject.remove_method(:method_missing)
+      1.__send__(:foo)
+    ensure
+      BasicObject.alias_method(:method_missing, :old_method_missing)
+      BasicObject.remove_method(:old_method_missing)
+    end
+  end
+end
+
+assert('Can still call super when BasicObject#method_missing is removed') do
+  assert_raise(TypeError) do
+    class A
+      def foo
+        super
+      end
+    end
+    begin
+      BasicObject.alias_method(:old_method_missing, :method_missing)
+      BasicObject.remove_method(:method_missing)
+      A.new.foo
+    ensure
+      BasicObject.alias_method(:method_missing, :old_method_missing)
+      BasicObject.remove_method(:old_method_missing)
+    end
+  end
+end