[NFC][AArch64] Handle processLogicalImmediate error

If processLogicalImmediate fails, we should return from the function
without changing InsInstrs or DelInstrs. This happens for
CodeGen/AArch64/urem-seteq-nonzero.ll LIT test as described in
https://reviews.llvm.org/D99662#2662296.

Callers of genAlternativeCodeSequence skip patterns where InsInstrs
stays empty, so this does not cause any issues now.

Differential Revision: https://reviews.llvm.org/D100047