Delete cached box art when the host is deleted

app/backend/computermanager.cpp

@@ -1,4 +1,5 @@
 #include "computermanager.h"
+#include "boxartmanager.h"
 #include "nvhttp.h"
 #include "settings/streamingpreferences.h"
 
@@ -399,6 +400,9 @@ public:
         // Delete the polling entry first. This will stop all polling threads too.
         delete pollingEntry;
 
+        // Delete cached box art
+        BoxArtManager::deleteBoxArt(m_Computer);
+
         // Finally, delete the computer itself. This must be done
         // last because the polling thread might be using it.
         delete m_Computer;