Handle bad extent type case
If we meet a bad extent type, find_updated_files is going
to print random things. Better warn the user about what
happens.
This fixes:
btrfs-list.c: Dans la fonction «find_updated_files» :
btrfs-list.c:668: attention : «disk_offset» may be used uninitialized in this function
btrfs-list.c:668: note: «disk_offset» was declared here
btrfs-list.c:667: attention : «disk_start» may be used uninitialized in this function
btrfs-list.c:667: note: «disk_start» was declared here
btrfs-list.c:666: attention : «len» may be used uninitialized in this function
btrfs-list.c:666: note: «len» was declared here
make: *** [btrfs-list.o] Erreur 1
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>