Fix: next 67 savegame versions are used in PatchPacks; skip them (#8411)

Various of PatchPacks (Spring 2013, Joker, ChillPP) used versions
slightly higher than ours. Of course, as time went by, this
caught up with us, and we are now almost pushing a new version
that would conflict with them. To avoid users creating unneeded
issues about "why can I not load my savegame", lets be ahead of
the curve and flat-out refuse to load them.

Version-wise, this is totally fine. We have ~32k versions to go
before we run out (0x8000 is masked by JGRPP; we should avoid
using that). At the rate we bump savegames, this is not going to
happen in any sane reality.

src/saveload/saveload.cpp

@@ -2689,6 +2689,7 @@ static SaveOrLoadResult DoLoad(LoadFilter *reader, bool load_check)
 
 			/* Is the version higher than the current? */
 			if (_sl_version > SAVEGAME_VERSION) SlError(STR_GAME_SAVELOAD_ERROR_TOO_NEW_SAVEGAME);
+			if (_sl_version >= SLV_START_PATCHPACKS && _sl_version <= SLV_END_PATCHPACKS) SlError(STR_GAME_SAVELOAD_ERROR_PATCHPACK);
 			break;
 		}