Squashfs: Fix oops when reading fsfuzzer corrupted filesystems

This fixes a code regression caused by the recent mainlining changes.
The recent code changes call zlib_inflate repeatedly, decompressing into
separate 4K buffers, this code didn't check for the possibility that
zlib_inflate might ask for too many buffers when decompressing corrupted
data.

Signed-off-by: Phillip Lougher <phillip@lougher.demon.co.uk>