Cancel throttled hover events when exiting hover modes

possibly related to #2736, as a source of "Uncaught Error Entity xxxx not found" errors

js/id/behavior/draw.js

@@ -116,6 +116,7 @@ iD.behavior.Draw = function(context) {
     }
 
     draw.off = function(selection) {
+        context.ui().sidebar.hover.cancel();
         context.uninstall(hover);
         context.uninstall(edit);
 

js/id/modes/browse.js

@@ -32,6 +32,7 @@ iD.modes.Browse = function(context) {
     };
 
     mode.exit = function() {
+        context.ui().sidebar.hover.cancel();
         behaviors.forEach(function(behavior) {
             context.uninstall(behavior);
         });

js/id/modes/drag_node.js

@@ -186,6 +186,7 @@ iD.modes.DragNode = function(context) {
     };
 
     mode.exit = function() {
+        context.ui().sidebar.hover.cancel();
         context.uninstall(hover);
         context.uninstall(edit);
 

js/id/ui/sidebar.js

@@ -12,8 +12,8 @@ iD.ui.Sidebar = function(context) {
         var inspectorWrap = selection.append('div')
             .attr('class', 'inspector-hidden inspector-wrap fr');
 
-        sidebar.hover = function(id) {
-            if (!current && id) {
+        function hover(id) {
+            if (!current && context.hasEntity(id)) {
                 featureListWrap.classed('inspector-hidden', true);
                 inspectorWrap.classed('inspector-hidden', false)
                     .classed('inspector-hover', true);
@@ -30,9 +30,9 @@ iD.ui.Sidebar = function(context) {
                 inspectorWrap.classed('inspector-hidden', true);
                 inspector.state('hide');
             }
-        };
+        }
 
-        sidebar.hover = _.throttle(sidebar.hover, 200);
+        sidebar.hover = _.throttle(hover, 200);
 
         sidebar.select = function(id, newFeature) {
             if (!current && id) {
@@ -73,6 +73,7 @@ iD.ui.Sidebar = function(context) {
     }
 
     sidebar.hover = function() {};
+    sidebar.hover.cancel = function() {};
     sidebar.select = function() {};
     sidebar.show = function() {};
     sidebar.hide = function() {};