Warn on invalid victory faction

[oznogon]

If neither side wins in Clash in Shangri-La, it attempts to declare victory for Independents, an invalid faction name (should be Independent). Fix this invalid faction name.

This changes the victory screen behavior for this outcome. Before, the game pauses with no victory message. After, the game pauses with a victory message for the Independent faction.

This behavior exposes another issue: functions used to find factions do not log when the passed faction name is invalid. Add warning logging when an invalid faction name is passed to Faction::find(), and error logging when an invalid faction name is passed to victory()

Example:

victory("Nobody")

results in no functional change in behavior, but adds logging to raise the issue:

[WARNING ]: Attempted to find faction named Nobody, but no faction name matched.
[ERROR   ]: Attempted to set victory faction to Nobody, but no faction name matched.