btrfs: Bypass unrelated items before accessing its contents in scrub

When we access extent_root in scrub_stripe() and
scrub_raid56_parity(), we need bypass unrelated tree item firstly
before using its contents to do other condition.

It is not a bug fix, only making code sequence in logic.
Signed-off-by: NZhao Lei <zhaolei@cn.fujitsu.com>
Signed-off-by: NChris Mason <clm@fb.com>

fs/btrfs/scrub.c

@@ -2856,6 +2856,10 @@ static noinline_for_stack int scrub_raid56_parity(struct scrub_ctx *sctx,
 			}
 			btrfs_item_key_to_cpu(l, &key, slot);
 
+			if (key.type != BTRFS_EXTENT_ITEM_KEY &&
+			    key.type != BTRFS_METADATA_ITEM_KEY)
+				goto next;
+
 			if (key.type == BTRFS_METADATA_ITEM_KEY)
 				bytes = root->nodesize;
 			else
@@ -2864,10 +2868,6 @@ static noinline_for_stack int scrub_raid56_parity(struct scrub_ctx *sctx,
 			if (key.objectid + bytes <= logic_start)
 				goto next;
 
-			if (key.type != BTRFS_EXTENT_ITEM_KEY &&
-			    key.type != BTRFS_METADATA_ITEM_KEY)
-				goto next;
-
 			if (key.objectid >= logic_end) {
 				stop_loop = 1;
 				break;
@@ -3193,6 +3193,10 @@ static noinline_for_stack int scrub_stripe(struct scrub_ctx *sctx,
 			}
 			btrfs_item_key_to_cpu(l, &key, slot);
 
+			if (key.type != BTRFS_EXTENT_ITEM_KEY &&
+			    key.type != BTRFS_METADATA_ITEM_KEY)
+				goto next;
+
 			if (key.type == BTRFS_METADATA_ITEM_KEY)
 				bytes = root->nodesize;
 			else
@@ -3201,10 +3205,6 @@ static noinline_for_stack int scrub_stripe(struct scrub_ctx *sctx,
 			if (key.objectid + bytes <= logical)
 				goto next;
 
-			if (key.type != BTRFS_EXTENT_ITEM_KEY &&
-			    key.type != BTRFS_METADATA_ITEM_KEY)
-				goto next;
-
 			if (key.objectid >= logical + map->stripe_len) {
 				/* out of this device extent */
 				if (key.objectid >= logic_end)