Add missing kRenderFx constant (#928)

* Add missing kRenderFx constant

* Change constant name to match SDK

Author: OciXCrom

plugins/include/amxconst.inc

@@ -341,6 +341,7 @@ enum
 	kRenderFxExplode,           /* Scale up really big! */
 	kRenderFxGlowShell,         /* Glowing Shell */
 	kRenderFxClampMinScale,     /* Keep this sprite from getting very small (SPRITES only!) */
+	kRenderFxLightMultiplier,   /* CTM !!!CZERO added to tell the studiorender that the value in iuser2 is a lightmultiplier */
 };
 
 /**