Checking a null URI scheme crashes Games
Here is the backtrace, from the master version:
#0 g_str_hash (v=0x0) at ghash.c:1955
#1 0x00007ffff7ccd39c in g_hash_table_lookup_node (hash_return=<synthetic pointer>, key=0x0,
hash_table=0x5555558afd20) at ghash.c:379
#2 g_hash_table_contains (hash_table=0x5555558afd20, key=0x0) at ghash.c:1343
#3 0x000055555557696a in games_game_collection_get_factories_for_uri_co (_data_=0x5555558035e0)
at /home/kekun/Projects/gnome-games/src/core/game-collection.vala:97