Made Ctrl turn off snapping if Snap to Fine Grid is enabled

Previously, it would cause it to switch to Snap to Grid. This left no
way of temporarily turning off snapping for people who usually snap to a
fine grid.

Closes mapeditor#2061

src/tiled/snaphelper.cpp

@@ -40,7 +40,7 @@ SnapHelper::SnapHelper(const MapRenderer *renderer,
 
 void SnapHelper::toggleSnap()
 {
-    mSnapToGrid = !mSnapToGrid;
+    mSnapToGrid = !(mSnapToGrid || mSnapToFineGrid);
     mSnapToFineGrid = false;
 }