More graceful error handling on failed savegame load

As outlined in #2005 i believe that trying to load a savegame followed by failing to do so should not render an entire game session useless (which is what it does currently).

The approach to fixing these errors is unconventional at best and I'm not sure myself i'd want to merge code like this into UH, but i at least wanted to bring some code into the discussion and maybe we can improve it from here or decide on different next steps.

Also will need someone to carefully look over the changes related to collector code, there's no way i could fully understand what i did there and judging from past experiences there always are corner cases not covered by testing. An example for this is the currently commented line 102 where i'm not sure what to do with it.

Note that while testing this currently is very easy (due to #2018) on my machine i was able to reliably freeze the UH process by aborting a load, confirming the popup, and then attempting to load the savegame again. Closing the "load game" window after the failed load and then loading the game would not freeze. I suspect an issue with my graphics driver since others were unable to reproduce.