ntfs3: avoid another -Wmaybe-uninitialized warning

The ntfs3 specific -Wmaybe-uninitialized flag found one more false-postive,
this time with gcc-10 on s390:

fs/ntfs3/frecord.c: In function 'ni_expand_list':
fs/ntfs3/frecord.c:1370:16: error: 'ins_attr' may be used uninitialized in this function [-Werror=maybe-uninitialized]

Add an explicit NULL pointer check before using the pointer, and
initialize it to NULL.

Fixes: 48d9b57 ("fs/ntfs3: add a subset of W=1 warnings for stricter checks")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Konstantin Komarov <almaz.alexandrovich@paragon-software.com>

Author: arndb

fs/ntfs3/frecord.c

@@ -1330,7 +1330,7 @@ int ni_expand_list(struct ntfs_inode *ni)
 {
 	int err = 0;
 	u32 asize, done = 0;
-	struct ATTRIB *attr, *ins_attr;
+	struct ATTRIB *attr, *ins_attr = NULL;
 	struct ATTR_LIST_ENTRY *le;
 	bool is_mft = ni->mi.rno == MFT_REC_MFT;
 	struct MFT_REF ref;
@@ -1363,7 +1363,7 @@ int ni_expand_list(struct ntfs_inode *ni)
 				      le16_to_cpu(attr->name_off), true,
 				      &ins_attr, NULL, NULL);
 
-		if (err)
+		if (err || !ins_attr)
 			goto out;
 
 		memcpy(ins_attr, attr, asize);