Fix call to nil block

The -[GBObjectiveCParser consumeMacro] method calls `[self.tokenizer consumeTo:@")" usingBlock:nil]` which eventually leads to a crash when calling the nil block. This behavior can be triggered with the `DEPRECATED_MSG_ATTRIBUTE` macro inside an enum, e.g. `UIBarStyleBlackOpaque DEPRECATED_MSG_ATTRIBUTE("Use UIBarStyleBlack") = 1`