Fix missing update to mixer channel name when created (#7795)

Fixes a regression from 07baf9e27a, in
which a channel that was created through a tracks "Assign track to new
mixer channel" context menu would display an incorrect name until it was
renamed by a user.

src/gui/MixerView.cpp

@@ -376,6 +376,7 @@ void MixerView::updateMixerChannel(int index)
 	}
 
 	thisLine->m_sendButton->updateLightStatus();
+	thisLine->m_renameLineEdit->setText(thisLine->elideName(thisLine->mixerChannel()->m_name));
 	thisLine->update();
 }