block: Detect multiplication overflow in bdrv_getlength

Bogus image may have a large total_sectors that will overflow the
multiplication. For cleanness, fix the return code so the error message
will be meaningful.
Reported-by: NRichard W.M. Jones <rjones@redhat.com>
Signed-off-by: NFam Zheng <famz@redhat.com>
Reviewed-by: NAlberto Garcia <berto@igalia.com>
Reviewed-by: NMarkus Armbruster <armbru@redhat.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

block.c

@@ -2341,6 +2341,7 @@ int64_t bdrv_getlength(BlockDriverState *bs)
 {
     int64_t ret = bdrv_nb_sectors(bs);
 
+    ret = ret > INT64_MAX / BDRV_SECTOR_SIZE ? -EFBIG : ret;
     return ret < 0 ? ret : ret * BDRV_SECTOR_SIZE;
 }