[PATCH] Fix vulnerabilities in BLX driver

[Even Rouault]

Henrik,

would you mind reviewing and testing the attached patch ? It should correct many vulnerabilities when opening corrupted BLX datasets. The most important changes are in decode_celldata().

I've also changed datasize and compdatasize to be unsigned values, as I've encountered datasize slightly above 32768 when trying to compress files where some tiles had big dynamics in values. With signed short, it turned to be a negative value when reading back the dataset.

There's also a small improvement with the progress callback being used by CreateCopy() code.

[Even Rouault]

Patch commited in r16627