Fix PPC_FP on non-sse4.1 code paths.

The Invalid bit on the x87 fpu is sticky, so once a single NaN goes
through the old code on CPUs without sse4.1 all future floats are
mutilated.

Patch to emulate PTEST by Fiora.

Should fix [issue 7237](https://code.google.com/p/dolphin-emu/issues/detail?id=7237) and [issue 7510](https://code.google.com/p/dolphin-emu/issues/detail?id=7510).