math.ceil/floor fix ported; "load quick" no longer boots you without a quick save

Commit bb557c on main ports a fix for math.ceil/math.floor, adds self checks for corrupted map files and stops the load command from booting you out of the session when the save is missing.

  • Port a fix for math.ceil/math.floor
  • Self checks for corrupted map files
  • load doesn't boot you from the session for missing saves, so an accidental "load quick" bind press is harmless
  • Fixed ZFunc not being set when overriding depth testing
  • Fixed a regression with DPanel:OnMousePressed due to recent changes
  • Merged PR: ENT:StoreOutput treats times=0 the same as times=-1