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: 9b7365fc1c82 ("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>
diff --git a/fs/ext4/ioctl.c b/fs/ext4/ioctl.c
index eae5917..0acf8ca 100644
--- a/fs/ext4/ioctl.c
+++ b/fs/ext4/ioctl.c
@@ -365,7 +365,7 @@
 		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)