clear select outlines on 1st scroll event on cartesian subplots

- see #2343 (comment)
  for more details on this issue.

Author: etpinard

src/plots/cartesian/dragbox.js

@@ -358,6 +358,10 @@ function makeDragBox(gd, plotinfo, x, y, w, h, ns, ew) {
             return;
         }
 
+        if(redrawTimer === null) {
+            clearSelect(zoomlayer);
+        }
+
         // If a transition is in progress, then disable any behavior:
         if(gd._transitioningWithDuration) {
             e.preventDefault();

test/jasmine/tests/select_test.js

@@ -530,6 +530,28 @@ describe('Test select box and lasso in general:', function() {
         .catch(fail)
         .then(done);
     });
+
+    it('scroll zoom should clear selection regions', function(done) {
+        var gd = createGraphDiv();
+        var mockCopy = Lib.extendDeep({}, mock);
+        mockCopy.layout.dragmode = 'select';
+        mockCopy.config = {scrollZoom: true};
+
+        Plotly.plot(gd, mockCopy).then(function() {
+            resetEvents(gd);
+            drag(selectPath);
+            return selectedPromise;
+        })
+        .then(function() {
+            mouseEvent('mousemove', selectPath[0][0], selectPath[0][1]);
+            mouseEvent('scroll', selectPath[0][0], selectPath[0][1], {deltaX: 0, deltaY: -20});
+        })
+        .then(function() {
+            assertSelectionNodes(0, 0);
+        })
+        .catch(fail)
+        .then(done);
+    });
 });
 
 describe('Test select box and lasso per trace:', function() {