jfs: add check read-only before truncation in jfs_truncate_nolock()

In the Linux kernel, the following vulnerability has been resolved: jfs: add check read-only before truncation in jfs_truncate_nolock() Added a check for "read-only" mode in the `jfs_truncate_nolock` function to avoid errors related to writing to a read-only filesystem. Call stack: block_write_begin() { jfs_write_failed() { jfs_truncate() { jfs_truncate_nolock() { txEnd() { ... log = JFS_SBI(tblk->sb)->log; // (log == NULL) If the `isReadOnly(ip)` condition is triggered in `jfs_truncate_nolock`, the function execution will stop, and no further data modification will occur. Instead, the `xtTruncate` function will be called with the "COMMIT_WMAP" flag, preventing modifications in "read-only" mode.