Compile cleanly with -Wunreachable-code

Based on Apple's recent security blunder, I turned **-Wunreachable-code** on in my projects. I found a couple places were MMDrawerController doesn't compile cleanly under this: one in the MMDrawerController.m, the other in the sample project. This pull request fixes both.

See: https://www.imperialviolet.org/2014/02/22/applebug.html