fix: abort search if we're already trying to download a pack

Meaning we don't have to wait for the searches to finish in the
background to finally start the modpack download, when we have already
selected it -_-

Signed-off-by: flow <flowlnlnln@gmail.com>

launcher/ui/pages/modplatform/ftb/FtbPage.h

@@ -78,6 +78,7 @@ public:
     void retranslate() override;
 
     void openedImpl() override;
+    void closedImpl() override;
 
     bool eventFilter(QObject * watched, QEvent * event) override;