BitUnStuff_Before_Lerc2v3(): avoid harmless unsigned-integer-overflow
BitUnStuff_Before_Lerc2v3(): avoid harmless unsigned-integer-overflow

c970d4a113dae004ce51f7a4c81e34d18b06b771 introduced an harmless
unsigned-integer-overflow. This is not a bug here, but GDAL uses the
-fsanitize=unsigned-integer-overflow OSSFuzz setting to detect real
issues, so let's avoid running into this situation.

Fixes https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=46564
Upstreaming of https://github.com/OSGeo/gdal/commit/85453c23e4fe645bb476c423a58b2049b6465a81

Esri/lerc,Esri/lerc,Esri/lerc,Esri/lerc,Esri/lerc,Esri/lerc,Esri/lerc