fixes mozilla#1013. dragging page elements

Author: dannycoates

app/controller.js

@@ -98,6 +98,9 @@ export default function(state, emitter) {
   });
 
   emitter.on('addFiles', async ({ files }) => {
+    if (files.length < 1) {
+      return;
+    }
     const maxSize = state.user.maxSize;
     state.archive = state.archive || new Archive();
     try {

app/dragManager.js

@@ -6,7 +6,12 @@ export default function(state, emitter) {
       }
     });
     document.body.addEventListener('drop', event => {
-      if (state.route === '/' && !state.uploading) {
+      if (
+        state.route === '/' &&
+        !state.uploading &&
+        event.dataTransfer &&
+        event.dataTransfer.files
+      ) {
         event.preventDefault();
         emitter.emit('addFiles', {
           files: Array.from(event.dataTransfer.files)