Fixed human module button finding

Added return values for EnumWindowsProc callback functions.

"To continue enumeration, the callback function must return TRUE; to stop enumeration, it must return FALSE."
http://msdn.microsoft.com/en-us/library/windows/desktop/ms633498(v=vs.85).aspx

Without the return values the human module doesn't find buttons that are deeper than 1 layer in the window tree.