add condition to check if active

fixes #6840
"setMap" registers listeners to dropArea, but it doesn't check whether "active" is true or false. Simply add condition to check "active".

src/ol/interaction/draganddrop.js

@@ -65,6 +65,8 @@ ol.inherits(ol.interaction.DragAndDrop, ol.interaction.Interaction);
  * @private
  */
 ol.interaction.DragAndDrop.handleDrop_ = function(event) {
+  var active = this.getActive();
+  if (active) {
     var files = event.dataTransfer.files;
     var i, ii, file;
     for (i = 0, ii = files.length; i < ii; ++i) {
@@ -74,6 +76,7 @@ ol.interaction.DragAndDrop.handleDrop_ = function(event) {
           this.handleResult_.bind(this, file));
       reader.readAsText(file);
     }
+  }
 };
 
 
@@ -82,9 +85,12 @@ ol.interaction.DragAndDrop.handleDrop_ = function(event) {
  * @private
  */
 ol.interaction.DragAndDrop.handleStop_ = function(event) {
+  var active = this.getActive();
+  if (active) {
     event.stopPropagation();
     event.preventDefault();
     event.dataTransfer.dropEffect = 'copy';
+  }
 };