SCUMM: (FM-TOWNS) - fix bug no. 12560 ("[FM Towns] scrolling much too…

… slow")

(partly revert fb8f108)

There is no simple solution that would still  leave the "butter smooth" scrolling for faster platforms intact. I have measured times between several code points to find any bottlenecks. My finding is that even single script opcodes may well take over 200ms to execute. And exceeding a singe 60 Hz tick happens way more often (which makes the scrolling fall behind and have to catch up, thus becoming a bit sloppy). So, for the "butter smooth" scrolling I'll probably implement a timer for the screen updates (which will then really behave much more like the interrupt handler of the original). But that's for a separate commit. This one is mostly about the bug ticket..

engines/scumm/gfx_towns.cpp

@@ -186,7 +186,7 @@ void ScummEngine::towns_updateGfx() {
 		return;
 
 	uint32 cur = _system->getMillis();
-	if (_scrollTimer <= cur) {
+	while (_scrollTimer <= cur) {
 		if (!_scrollTimer)
 			_scrollTimer = cur;
 		_scrollTimer += 1000 / 60;