ext4: fix an ext3 collapse range regression in xfstests

The xfstests test suite assumes that an attempt to collapse range on
the range (0, 1) will return EOPNOTSUPP if the file system does not
support collapse range.  Commit 280227a75b56: "ext4: move check under
lock scope to close a race" broke this, and this caused xfstests to
fail when run when testing file systems that did not have the extents
feature enabled.

Reported-by: Eric Whitney <enwlinux@gmail.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index 451b92a..e003a1e 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -5396,6 +5396,14 @@
 	loff_t new_size, ioffset;
 	int ret;
 
+	/*
+	 * We need to test this early because xfstests assumes that a
+	 * collapse range of (0, 1) will return EOPNOTSUPP if the file
+	 * system does not support collapse range.
+	 */
+	if (!ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS))
+		return -EOPNOTSUPP;
+
 	/* Collapse range works only on fs block size aligned offsets. */
 	if (offset & (EXT4_CLUSTER_SIZE(sb) - 1) ||
 	    len & (EXT4_CLUSTER_SIZE(sb) - 1))