Addendum to emergency fix

Ensure vim_message() outputs an empty message when the Ruby string has
length 0.  Failing to do this will cause the message area not to clear
when it should.

src/if_ruby.c

@@ -773,6 +773,10 @@ static VALUE vim_message(VALUE self UNUSED, VALUE str)
 	if (p) *p = '\0';
 	MSG(buff);
     }
+    else
+    {
+	MSG("");
+    }
     return Qnil;
 }