Stop execution when performing HIO request

Since the HIO request is basically treated like a syscall, we need to
stop emulation while waiting for the GDB client to reply with the
result. This ensures any memory queries etc. that GDB makes to fulfill
the HIO request are accessing memory as it was at the time of the
request, instead of afterwards.

src/core/hle/kernel/svc.cpp

@@ -1144,6 +1144,11 @@ void SVC::Break(u8 break_reason) {
 /// Used to output a message on a debug hardware unit, or for the GDB HIO
 // protocol - does nothing on a retail unit.
 void SVC::OutputDebugString(VAddr address, s32 len) {
+    if (!Memory::IsValidVirtualAddress(*kernel.GetCurrentProcess(), address)) {
+        LOG_WARNING(Kernel_SVC, "OutputDebugString called with invalid address {:X}", address);
+        return;
+    }
+
     if (len == 0) {
         GDBStub::SetHioRequest(address);
         return;