More silence under valgrind

This patch prevents valgrind messages like this:

==3751== Conditional jump or move depends on uninitialised value(s)
==3751==    at 0x6BBA16: vt_input::InputEngine::_SetNewJoyButton(unsigned char&, unsigned char) (in ./valyriatear)
==3751==    by 0x885BBC: LoadSettings() (in ./valyriatear)
==3751==    by 0x888661: InitializeEngine() (in ./valyriatear)
==3751==    by 0x6031CE: main (in ./valyriatear)