iso9660: Fix buffer overflow on unaligned accesses

! iso9660: If we start reading in the middle of a cache block, we must
  not try to copy a whole block, but stop at the end of the cache
  block.
Signed-off-by: Kevin Wolf <kevin@tyndur.org>

iso9660/sector.c

@@ -66,7 +66,7 @@ size_t iso9660_read(struct iso9660_fs_res *res,size_t pos,size_t size,void *buff
         break;
     }
 
-    cur_size = MIN(rem_size, res->voldesc->sector_size);
+    cur_size = MIN(rem_size, res->voldesc->sector_size - offset);
 
     memcpy(buffer,cache_block->data+offset,cur_size);
     cdi_cache_block_release(res->cache,cache_block);