UploadArea should only preventDefault for Escape

This will make accessibility for some things less effortful, since we won't have to define a prior event handler to do whatever should be happening by default.

app/javascript/mastodon/features/ui/components/upload_area.js

@@ -12,13 +12,12 @@ export default class UploadArea extends React.PureComponent {
   };
 
   handleKeyUp = (e) => {
-    e.preventDefault();
-    e.stopPropagation();
-
     const keyCode = e.keyCode;
     if (this.props.active) {
       switch(keyCode) {
       case 27:
+        e.preventDefault();
+        e.stopPropagation();
         this.props.onClose();
         break;
       }