Fixed frameskip for games using manual erase.

I know you all love those random changes in "manual modes"...
so here's another one... :[

This one fixes frameskip for at least Panzer Dragoon (the first)
but maybe others... and it doesn't break King the Spirits (the
game for which I added manual erase in the first place...)

git-svn-id: https://yabause.svn.sourceforge.net/svnroot/yabause/trunk@3072 d7be59e3-070e-4b9a-85a1-4646befae34d