fix SDL_GetSensorInstanceID() return code upon failure.

Reference issue: https://github.com/libsdl-org/SDL/issues/7051

include/SDL3/SDL_sensor.h

@@ -223,7 +223,7 @@ extern DECLSPEC int SDLCALL SDL_GetSensorNonPortableType(SDL_Sensor *sensor);
  * Get the instance ID of a sensor.
  *
  * \param sensor The SDL_Sensor object to inspect
- * \returns the sensor instance ID, or -1 if `sensor` is NULL.
+ * \returns the sensor instance ID, or 0 if `sensor` is NULL.
  *
  * \since This function is available since SDL 3.0.0.
  */

src/sensor/SDL_sensor.c

@@ -374,7 +374,7 @@ int SDL_GetSensorNonPortableType(SDL_Sensor *sensor)
 SDL_SensorID SDL_GetSensorInstanceID(SDL_Sensor *sensor)
 {
     if (!SDL_IsSensorValid(sensor)) {
-        return -1;
+        return 0;
     }
 
     return sensor->instance_id;