UI: Reset replay buffer button on "stop" signal

Fixes an issue when Start Replay Button stays at checked state if stop
signal generated (hotkey event for example) instead of mouse click.

Mantis: https://obsproject.com/mantis/view.php?id=1343

UI/window-basic-main.cpp

@@ -5399,6 +5399,7 @@ void OBSBasic::ReplayBufferStop(int code)
 		return;
 
 	replayBufferButton->setText(QTStr("Basic.Main.StartReplayBuffer"));
+	replayBufferButton->setChecked(false);
 
 	if (sysTrayReplayBuffer)
 		sysTrayReplayBuffer->setText(replayBufferButton->text());