PyByteArray_Resize() failure: leave the bytearray object in an consistent state.

If growth < 0, handling the memory allocation failure is tricky here because
the bytearray object has already been modified.  If lo != 0, the operation is
completed, but a MemoryError is still raised and the memory block is not
shrinked. If lo == 0, the bytearray is restored in its previous state and a
MemoryError is raised.