fix: ensure liveupdate pubsubs exit (#5557)

Previously, the derived class (i.e. BttvLiveUpdates or SeventvEventAPI)
    would have their destructor ran before BasicPubSubManager called
    stop, meaning there was a time wherein messages could still flow
    through, attempting to call `onMessage` on a pure virtual, causing a
    crash.

src/providers/bttv/BttvLiveUpdates.cpp

@@ -15,6 +15,11 @@ BttvLiveUpdates::BttvLiveUpdates(QString host)
 {
 }
 
+BttvLiveUpdates::~BttvLiveUpdates()
+{
+    this->stop();
+}
+
 void BttvLiveUpdates::joinChannel(const QString &channelID,
                                   const QString &userName)
 {

src/providers/bttv/BttvLiveUpdates.hpp

@@ -19,6 +19,7 @@ class BttvLiveUpdates : public BasicPubSubManager<BttvLiveUpdateSubscription>
 
 public:
     BttvLiveUpdates(QString host);
+    ~BttvLiveUpdates() override;
 
     struct {
         Signal<BttvLiveUpdateEmoteUpdateAddMessage> emoteAdded;