Add umineko spsize behavior and save/load fixes

[drojf]

This PR fixes the following issues:

Graphics bugs with spsize command when using 2x mode

• https://github.com/07th-mod/ponscripter-fork/issues/6 fixed by 4a23c2a

Save/load related fixes

• Fix the game launching even after error message is displayed telling you to restart the game. When this happened, it would use a save location you probably didn't intend. Now game will quit under this condition. c39f728
  • Fix unable to save/load in certain cases due to lack of null terminator f31bff9
  • Add some niceties for save/load behavior 56e1f1e 92459a1