AGS: Fix undefined behavior in initialization of AGSSnowRain

Due to the declaration order of the member variables, the _screenWidth
and _screenHeight where used before being initialized to initialize
the _snow and _rain variables. This could then lead to a division by
zero.

This fixes bug #12771: AGS King's Quest 3 VGA from IA crashes on startup

engines/ags/plugins/ags_snow_rain/ags_snow_rain.h

@@ -37,11 +37,11 @@ namespace AGSSnowRain {
 class AGSSnowRain : public PluginBase {
 	SCRIPT_HASH(AGSSnowRain)
 private:
-	Weather _rain;
-	Weather _snow;
 	int32 _screenWidth = 320;
 	int32 _screenHeight = 200;
 	int32 _screenColorDepth = 32;
+	Weather _rain;
+	Weather _snow;
 
 private:
 	void srSetWindSpeed(ScriptMethodParams &params);