liblzma: lzma_index_append: Add missing integer overflow check.

liblzma: lzma_index_append: Add missing integer overflow check.

The documentation in src/liblzma/api/lzma/index.h suggests that
both the unpadded (compressed) size and the uncompressed size
are checked for overflow, but only the unpadded size was checked.
The uncompressed check is done first since that is more likely to
occur than the unpadded or index field size overflows.