btrfs-progs: fix superblock range exclusion check

[BUG]
For certain btrfs images, a BUG_ON() can be triggered at open_ctree()
time:

  Opening filesystem to check...
  extent_io.c:158: insert_state: BUG_ON `end < start` triggered, value 1
  btrfs(+0x2de57)[0x560c4d7cfe57]
  btrfs(+0x2e210)[0x560c4d7d0210]
  btrfs(set_extent_bits+0x254)[0x560c4d7d0854]
  btrfs(exclude_super_stripes+0xbf)[0x560c4d7c65ff]
  btrfs(btrfs_read_block_groups+0x29d)[0x560c4d7c698d]
  btrfs(btrfs_setup_all_roots+0x3f3)[0x560c4d7c0b23]
  btrfs(+0x1ef53)[0x560c4d7c0f53]
  btrfs(open_ctree_fs_info+0x90)[0x560c4d7c11a0]
  btrfs(+0x6d3f9)[0x560c4d80f3f9]
  btrfs(main+0x94)[0x560c4d7b60c4]
  /usr/lib/libc.so.6(__libc_start_main+0xf3)[0x7fd189773ee3]
  btrfs(_start+0x2e)[0x560c4d7b635e]

[CAUSE]
This is caused by passing @len == 0 to add_excluded_extent(), which
means one reverse mapped range is just out of the block group range,
normally means a by-one error.

[FIX]
Fix the boundary check on the reserve mapped range against block group
range.  If a reverse mapped super block starts at the end of the block
group, it doesn't cover so we don't need to bother the case.

Issue: #210
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

extent-tree.c

@@ -3640,7 +3640,7 @@ int exclude_super_stripes(struct btrfs_fs_info *fs_info,
 		while (nr--) {
 			u64 start, len;
 
-			if (logical[nr] > cache->key.objectid +
+			if (logical[nr] >= cache->key.objectid +
 			    cache->key.offset)
 				continue;