skip of traces that don't exist in Fx.hover()

- this used to result in:
  'TypeError: Cannot read property '0' of undefined'

Author: etpinard

src/components/fx/hover.js

@@ -330,12 +330,14 @@ function _hover(gd, evt, subplot, noHoverEvent) {
         // user specified an array of points to highlight
         hovermode = 'array';
         for(itemnum = 0; itemnum < evt.length; itemnum++) {
-            cd = gd.calcdata[evt[itemnum].curveNumber||0];
-            trace = cd[0].trace;
-            if(cd[0].trace.hoverinfo !== 'skip') {
-                searchData.push(cd);
-                if(trace.orientation === 'h') {
-                    hasOneHorizontalTrace = true;
+            cd = gd.calcdata[evt[itemnum].curveNumber || 0];
+            if(cd) {
+                trace = cd[0].trace;
+                if(cd[0].trace.hoverinfo !== 'skip') {
+                    searchData.push(cd);
+                    if(trace.orientation === 'h') {
+                        hasOneHorizontalTrace = true;
+                    }
                 }
             }
         }

test/jasmine/tests/finance_test.js

@@ -1241,6 +1241,17 @@ describe('finance trace hover via Fx.hover():', function() {
                     name: ['trace 0', 'trace 1']
                 }, 'hover over 3rd items (aka 2nd visible items)');
             })
+            .then(function() {
+                Lib.clearThrottle();
+                return Plotly.react(gd, [gd.data[0]], gd.layout);
+            })
+            .then(function() { hover(281, 252); })
+            .then(function() {
+                assertHoverLabelContent({
+                    nums: 'hover off by 1\nopen: 7\nhigh: 7\nlow: 7\nclose: 7  ▲',
+                    name: ''
+                }, 'after removing 2nd trace');
+            })
             .catch(failTest)
             .then(done);
         });