Fix being able to open Labels dropdown even if there are no labels

The issue is being able to open labels dropdown even if there are no
labels.
Resolved by only showing dropdown if there are any labels found.

close #8141

src/mail-app/mail/view/MailView.ts

@@ -575,12 +575,13 @@ export class MailView extends BaseTopLevelView implements TopLevelView<MailViewA
 	 */
 	private labels() {
 		const mailList = this.mailViewModel.listModel
-		if (mailList == null) {
+		if (mailList == null || !mailLocator.mailModel.canAssignLabels()) {
 			return
 		}
-
+		const labels = mailLocator.mailModel.getLabelStatesForMails(mailList.getSelectedAsArray())
 		const selectedMails = mailList.getSelectedAsArray()
-		if (isEmpty(selectedMails)) {
+
+		if (isEmpty(labels) || isEmpty(selectedMails)) {
 			return
 		}