Return true after queueing a guest syscall override

dispatchSyscallOverride returns bool, and its caller uses that to
decide whether the built-in handler still needs to run. The success
path -- the one that actually queues the guest's handler as an
invocation -- fell off the end of the function without returning.

That is undefined behaviour, and the practical failure mode is bad:
whatever happened to be in the return register decided whether the
built-in syscall ran in addition to the guest's override, so a game
that overrides a syscall could get the effect applied twice, or not at
all, depending on the build.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

ps2xRuntime/src/lib/Kernel/Syscalls/System.cpp

@@ -440,6 +440,11 @@ namespace ps2_syscalls
             parent.r[2] = completed.r[2];
         };
         scheduler.invokeCurrent(std::move(invocation));
+        // The invocation is queued and the caller must not fall through to the
+        // built-in handler. Falling off the end of a non-void function here was
+        // undefined behaviour: whatever happened to be in the return register
+        // decided whether the built-in ran as well as the guest's override.
+        return true;
     }
 
     static bool tryResolveGuestSyscallMirrorAddr(uint32_t syscallIndex, uint32_t &guestAddr)