[xswiftbus] Stop logging probe failures after a certain number

To avoid flooding the log with messages.

src/xswiftbus/terrainprobe.h

@@ -39,6 +39,7 @@ namespace XSwiftBus
 
     private:
         XPLMProbeRef m_ref = nullptr;
+        mutable int m_logMessageCount = 0;
     };
 } // ns