btrfs-progs: convert: fix buggy logic in create_image_file_range()

When checking if the requested range starts in a valid region but later
hits a reserved range, we require the reserved range to end before the
requested one does.

This is incorrect. Since we're going to truncate the requested range
anyway, we want this check to pass even if the requested range ends
partway through a reserved range.

Fix the issue by checking against the reserved range's start address
instead of its end.

Luckily, I don't believe this bug makes a difference in the current code
path, since the range we pass to this function never ends before the end
of the filesystem.

Issue: #297
Issue: #349
Author: Thomas Hebb <tommyhebb@gmail.com>
Pull-request: #494
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

convert/main.c

@@ -256,10 +256,13 @@ static int create_image_file_range(struct btrfs_trans_handle *trans,
 		/*
 		 *      |-- reserved --|
 		 * |-- range --|
+		 * or
+		 *      |-- reserved --|
+		 * |------- range -------|
 		 * Leading part may still create a file extent
 		 */
 		if (bytenr < reserved->start &&
-		    bytenr + len >= range_end(reserved)) {
+		    bytenr + len > reserved->start) {
 			len = min_t(u64, len, reserved->start - bytenr);
 			break;
 		}