Upload: check if locked before confirming delete

## Reproduce
Have 2 tabs + paused upload
Open "cancel" dialog in one of the tabs.
Continue upload in other tab
Confirm cancellation in first tab
Upload disappears from both tabs, but based on network traffic the upload keeps happening.
(If upload finishes the claim seems to get created)

ui/component/webUploadList/internal/web-upload-item.jsx

@@ -46,6 +46,12 @@ export default function WebUploadItem(props: Props) {
       subtitle: __('Cancel and remove the selected upload?'),
       body: params.name ? <p className="empty">{`lbry://${params.name}`}</p> : undefined,
       onConfirm: (closeModal) => {
+        if (tusIsSessionLocked(params.guid)) {
+          // Corner-case: it's possible for the upload to resume in another tab
+          // after the modal has appeared. Make a final lock-check here.
+          // We can invoke a toast here, but just do nothing for now.
+          // The upload status should make things obvious.
+        } else {
           if (uploader) {
             if (resumable) {
               // $FlowFixMe - couldn't resolve to TusUploader manually.
@@ -57,6 +63,7 @@ export default function WebUploadItem(props: Props) {
 
           // The second parameter (params) can be removed after January 2022.
           doUpdateUploadRemove(params.guid, params);
+        }
         closeModal();
       },
     });