Do not show drag&drop dialog when not logined (#20400)

* Cannot upload until login

* and do not fire upload

* change username props to context

app/javascript/mastodon/features/ui/index.js

@@ -290,7 +290,7 @@ class UI extends React.PureComponent {
       this.dragTargets.push(e.target);
     }
 
-    if (e.dataTransfer && Array.from(e.dataTransfer.types).includes('Files') && this.props.canUploadMore) {
+    if (e.dataTransfer && Array.from(e.dataTransfer.types).includes('Files') && this.props.canUploadMore && this.context.identity.signedIn) {
       this.setState({ draggingOver: true });
     }
   }
@@ -318,7 +318,7 @@ class UI extends React.PureComponent {
     this.setState({ draggingOver: false });
     this.dragTargets = [];
 
-    if (e.dataTransfer && e.dataTransfer.files.length >= 1 && this.props.canUploadMore) {
+    if (e.dataTransfer && e.dataTransfer.files.length >= 1 && this.props.canUploadMore && this.context.identity.signedIn) {
       this.props.dispatch(uploadCompose(e.dataTransfer.files));
     }
   }