fix: console error when hovering over empty gutter cell with tooltipFollowsMouse set to false (#5173)

Fixes bug where console error is thrown when hovering over a gutter cell without content when tooltipFollowsMouse set to false.

Author: akoreman

src/mouse/default_gutter_handler.js

@@ -49,6 +49,9 @@ function GutterHandler(mouseHandler) {
 
         tooltip.showTooltip(row);
 
+        if (!tooltip.isOpen)
+            return;
+
         editor.on("mousewheel", hideTooltip);
 
         if (mouseHandler.$tooltipFollowsMouse) {