Move general oldxp/oldyp updating to just before gameinput()

This has to be done in order to fix rendering when on a conveyor or
moving platform and actively moving with or against it. Pretty sure this
shouldn't break anything, oldxp/oldyp is mostly visual after all (and by
the time it's used for gravity line collision checking,
updateentitylogic() would've already gotten around to it anyway).

Incidentally, this also fixes a jitter that would occur if you were
moving at the time you died or collected a trinket or custom crewmate,
due to the game temporarily freezing and either doing deathsequence or
completestop.

desktop_version/src/main.cpp

@@ -417,6 +417,13 @@ int main(int argc, char *argv[])
                         script.run();
                     }
 
+                    //Update old positions of entities - has to be done BEFORE gameinput!
+                    for (size_t i = 0; i < obj.entities.size(); i++)
+                    {
+                        obj.entities[i].oldxp = obj.entities[i].xp;
+                        obj.entities[i].oldyp = obj.entities[i].yp;
+                    }
+
                     gameinput();
                     gamelogic();