HAL_SITL: fixed undefined behaviour in GPIO

libraries/AP_HAL_SITL/GPIO.cpp

@@ -29,6 +29,9 @@ uint8_t GPIO::read(uint8_t pin)
     if (!_sitlState->_sitl) {
         return 0;
     }
+    if (!valid_pin(pin)) {
+        return 0;
+    }
     
     // weight on wheels pin support
     if (pin == _sitlState->_sitl->wow_pin.get()) {
@@ -45,6 +48,9 @@ void GPIO::write(uint8_t pin, uint8_t value)
         return;
     }
 
+    if (!valid_pin(pin)) {
+        return;
+    }
     if (pin < 8) {
         if (!(pin_mode_is_write & (1U<<pin))) {
             // ignore setting of pull-up resistors