Fix scatterplot selection performance

PR #5038 introduced jittering suspension with selection. It introduced a
performance regression, because it needlessly updated point positions
while the selection was being performed. For example, with 10000 data
points, selection was lagging noticeably.

Orange/widgets/visualize/owscatterplotgraph.py

@@ -642,12 +642,16 @@ def update_tooltip(self, modifiers=Qt.NoModifier):
         self.tip_textitem.setHtml(text)
 
     def suspend_jittering(self):
+        prev_state = self.jittering_suspended
         self.jittering_suspended = True
-        self.update_jittering()
+        if prev_state != self.jittering_suspended and self.jitter_size != 0:
+            self.update_jittering()
 
     def unsuspend_jittering(self):
+        prev_state = self.jittering_suspended
         self.jittering_suspended = False
-        self.update_jittering()
+        if prev_state != self.jittering_suspended and self.jitter_size != 0:
+            self.update_jittering()
 
     def update_jittering(self):
         x, y = self.get_coordinates()