arp: Prevent uninitialized read of launch member variable

If anything happened to call arp functions in the wrong order and called
IRegistrar's Issue function before SetApplicationLaunchProperty, we'd
read from an uninitialized ApplicationLaunchProperty instance.

Instead, we can always initialize it so if this does happen, then the
outcome of doing such a thing is at least consistently reproducible.

src/core/hle/service/glue/arp.cpp

@@ -240,7 +240,7 @@ private:
 
     std::function<ResultCode(u64, ApplicationLaunchProperty, std::vector<u8>)> issue_process_id;
     bool issued = false;
-    ApplicationLaunchProperty launch;
+    ApplicationLaunchProperty launch{};
     std::vector<u8> control;
 };