[FREETYPE] Handle allocation failures in our stack-saving hacks. CORE-15642

[FREETYPE] Handle allocation failures in our stack-saving hacks. CORE-15642

Running out of pool is likely at least during kmtest:ExPools.
There is a chance of crashing when dereferencing these null pointers -- but
worse, there's also a chance of overwriting the IVT or BDA if a VDM BIOS
call is in progress, which can lead to crashes in non-obvious places later.