ext4: make ext4_ext_convert_to_initialized() return proper number of blocks

ext4_ext_convert_to_initialized() can return more blocks than are
actually allocated from map->m_lblk in case where initial part of the
on-disk extent is zeroed out. Luckily this doesn't have serious
consequences because the caller currently uses the return value
only to unmap metadata buffers. Anyway this is a data
corruption/exposure problem waiting to happen so fix it.

Coverity-id: 1226848
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

fs/ext4/extents.c

@@ -3603,11 +3603,10 @@ static int ext4_ext_convert_to_initialized(handle_t *handle,
 		}
 	}
 
-	allocated = ext4_split_extent(handle, inode, ppath,
-				      &split_map, split_flag, flags);
-	if (allocated < 0)
-		err = allocated;
-
+	err = ext4_split_extent(handle, inode, ppath, &split_map, split_flag,
+				flags);
+	if (err > 0)
+		err = 0;
 out:
 	/* If we have gotten a failure, don't zero out status tree */
 	if (!err)