tif_lzw.c: avoid warning about misaligned address with UBSAN (fixes #616)
The branch suppressed by this commit wasn't useful as I've verified that with -O2 and -O3 and gcc or clang, doing a memcpy() + _byteswap_uint64() generates exactly the same code as _byteswap_uint64(*ptr). The warning with UBSAN thus only comes from UBSAN generating special code to catch the misalignment, but is unlikely to cause any issue in practice given the above observation.