ext4: fix uniniatilized extent splitting error

Fix bug reported by Dmitry Monakhov caused by lost error code

    Testcase: 

    blksize = 0x1000;
    fd = open(argv[1], O_RDWR|O_CREAT, 0700);
    unsigned long long sz = 0x10000000UL;
    /* allocating big blocks chunk */
    syscall(__NR_fallocate, fd, 0, 0UL, sz)

    /* grab all other available filesystem space */
    tfd = open("tmp", O_RDWR|O_CREAT|O_DIRECT, 0700);
    while( write(tfd, buf, 4096) > 0); /* loop untill ENOSPC */
    fsync(fd); /* just in case */
    while (pos < sz) {
    	/* each seek+ write operation result in splits uninitialized extent
    	in three extents. Splitting may result in new extent allocation
    	which probably will fail because of ENOSPC*/

    	lseek(fd, blksize*2 -1, SEEK_CUR);
    	if ((ret = write(fd, 'a', 1)) != 1)
    		exit(1);
    	pos += blksize * 2;
    }
Signed-off-by: NDmitry Monakhov <dmonakhov@openvz.org>
Signed-off-by: NMingming Cao <cmm@us.ibm.com>
Signed-off-by: N"Theodore Ts'o" <tytso@mit.edu>

fs/ext4/extents.c

@@ -2373,9 +2373,10 @@ int ext4_ext_get_blocks(handle_t *handle, struct inode *inode,
 			ret = ext4_ext_convert_to_initialized(handle, inode,
 								path, iblock,
 								max_blocks);
-			if (ret <= 0)
+			if (ret <= 0) {
+				err = ret;
 				goto out2;
-			else
+			} else
 				allocated = ret;
 			goto outnew;
 		}