udf: refactor inode_bmap() to handle error

In the Linux kernel, the following vulnerability has been resolved: udf: refactor inode_bmap() to handle error Refactor inode_bmap() to handle error since udf_next_aext() can return error now. On situations like ftruncate, udf_extend_file() can now detect errors and bail out early without resorting to checking for particular offsets and assuming internal behavior of these functions.