Fix default game fallback in _restore_game_info

[DasSkelett]

Problem

Noticed the following error in the syslog when navigating to the mod update upload page on alpha:

 2020-05-22 11:02:31,965 ERROR Backend:30011 Exception on /mod/3/Test download path/update [GET]
 Traceback (most recent call last):
   File "/var/www/virtual/spacedock.info/htdocs/SpaceDock/lib/python3.8/site-packages/sqlalchemy/engine/base.py", line 1283, in _execute_context
     self.dialect.do_execute(
   File "/var/www/virtual/spacedock.info/htdocs/SpaceDock/lib/python3.8/site-packages/sqlalchemy/engine/default.py", line 590, in do_execute
     cursor.execute(statement, parameters)
 psycopg2.errors.InvalidTextRepresentation: invalid input syntax for integer: "kerbal-space-program"
 LINE 3: WHERE game.id = 'kerbal-space-program' ORDER BY game.id DESC...

<some more messages and lines and stuff>

   File "/var/www/virtual/spacedock.info/htdocs/SpaceDock/KerbalStuff/blueprints/mods.py", line 62, in update
     ga = _restore_game_info()
   File "/var/www/virtual/spacedock.info/htdocs/SpaceDock/KerbalStuff/blueprints/mods.py", line 40, in _restore_game_info
     ga = Game.query.filter(Game.id == game_id).order_by(desc(Game.id)).first()

If users have no game assigned to their current session, _restore_game_info() tries to default to KSP.
However, it assigns the game's short instead of the id to the game_id variable, and then the DB throws a type error.

The return value hasn't been used in update.html, and in create.html only for setting the default selection I think.

Changes

_restore_game_info() is now changed to properly fallback to KSP (based on the short).

The call to _restore_game_info() is removed from update() since it isn't needed, the game is also no longer passed to the template.

In api.update_mod a query filter has been changed to compare against mod.game_id instead of Mod.game_id. Not sure why this even worked, I guess SQLAlchemy has some special logic for comparing to classes/table columns, and just tests if the columns are of the same type or something.

The game parameter for create.html has been renamed to games, since it's a list of games, not a single one.

[HebaruSan]

That makes a lot more sense now.