plugins/zoom: limit the maximum zoom value to 100

Accidental changes in zoom can become very time consuming to undo otherwise.
With a value of 100, you can still zoom in far enough to only see a few pixels
on the screen, so it shouldn't break any actual use cases

BUG: 485192

src/plugins/zoom/zoom.cpp

@@ -456,6 +456,7 @@ void ZoomEffect::zoomIn(double to)
     } else {
         target_zoom = to;
     }
+    target_zoom = std::min(target_zoom, 100.0);
     if (!polling) {
         polling = true;
         effects->startMousePolling();