ext4: fix check of dqget() return value in ext4_ioctl_setproject()

A failed call to dqget() returns an ERR_PTR() and not null. Fix
the check in ext4_ioctl_setproject() to handle this correctly.

Fixes: 9b7365fc ("ext4: add FS_IOC_FSSETXATTR/FS_IOC_FSGETXATTR interface support")
Cc: stable@vger.kernel.org # v4.5
Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Jan Kara <jack@suse.cz>

fs/ext4/ioctl.c

@@ -365,7 +365,7 @@ static int ext4_ioctl_setproject(struct file *filp, __u32 projid)
 		struct dquot *transfer_to[MAXQUOTAS] = { };
 
 		transfer_to[PRJQUOTA] = dqget(sb, make_kqid_projid(kprojid));
-		if (transfer_to[PRJQUOTA]) {
+		if (!IS_ERR(transfer_to[PRJQUOTA])) {
 			err = __dquot_transfer(inode, transfer_to);
 			dqput(transfer_to[PRJQUOTA]);
 			if (err)