Fix two places with map.oldypos not being assigned

These places didn't assign map.oldypos when they assigned map.ypos. This
could have only resulted in visual glitches, but it's good to be
consistent and proactively fix these.

desktop_version/src/Script.cpp

@@ -2705,6 +2705,7 @@ void scriptclass::startgamemode( int t )
 			if (INBOUNDS_VEC(i, obj.entities))
 			{
 				map.ypos = obj.entities[i].yp - 120;
+				map.oldypos = map.ypos;
 			}
 			graphics.towerbg.bypos = map.ypos / 2;
 			map.cameramode = 0;

desktop_version/src/main.cpp

@@ -494,6 +494,7 @@ int main(int argc, char *argv[])
     map.nexttowercolour();
 
     map.ypos = (700-29) * 8;
+    map.oldypos = map.ypos;
     graphics.towerbg.bypos = map.ypos / 2;
     graphics.titlebg.bypos = map.ypos / 2;