Quickfix of strange issue where left drawer gets blank

https://github.com/mutualmobile/MMDrawerController/issues/30

For some reason self.centerContainerView.frame.origin.x is sometimes being set to 0.5 at the end of close animation. This causes drawerFullyCovered to be incorrectly set to false. 

Note: This is just a quickfix. The actual reason of why origin.x is being set to 0.5 in the first place should be investigated and corrected in a future version.