btrfs-progs: Fix a buffer overflow causing segfault in fstests/btrfs/069

btrfs-progs: Fix a buffer overflow causing segfault in fstests/btrfs/069

The newly introduced search_chunk_tree_for_fs_info() won't count devid 0
in fi_arg->num_devices, which will cause buffer overflow since later
get_device_info() will fill di_args with devid.

This can be trigger by fstests/btrfs/069 and any operations needs to
iterate over all the devices like 'fi show' or 'dev stat' while
replacing.

The fix is do an extra probe specifically for devid 0 after
search_chunk_tree_for_fs_info() and change num_devices if needed.

Reported-by: Tsutomu Itoh <t-itoh@jp.fujitsu.com>
Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
Signed-off-by: Gui Hecheng <guihc.fnst@cn.fujitsu.com>
Signed-off-by: David Sterba <dsterba@suse.cz>