Attempt to fix crash when reloading core on static builds

Created by: jdgleaver

At present, the core will crash the second time content is loaded when using a static build (Switch, etc.). I don't have any supported hardware to test this on, but by building under Linux using the --enable-preserve_dylib configure option I was able reproduce a segfault and graphical corruption caused by static variables carrying over incorrect values from the previous run.

This trivial PR 'resets' these static variables appropriately. I hope this will fix issue #215 (closed) - if anyone could test a static build, I would be grateful!