make draggingOver state off correctly (#9797)

* make draggingOver stat off correctly

* ignore safari and Edge

* Revert "ignore safari and Edge"

This reverts commit b9b93ea3674877670161207a3f9b3a4f82b68a2d.

* Revert "make draggingOver stat off correctly"

This reverts commit f5fd6b94dc1d4b812e0b910b2b4f35792c3ea3a1.

* clear drag stack when drop

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

@@ -259,6 +259,7 @@ class UI extends React.PureComponent {
     e.preventDefault();
 
     this.setState({ draggingOver: false });
+    this.dragTargets = [];
 
     if (e.dataTransfer && e.dataTransfer.files.length === 1) {
       this.props.dispatch(uploadCompose(e.dataTransfer.files));