Fix env_spark transitioning to other maps when it shouldn't

Resolves ValveSoftware/halflife#3280

dlls/buttons.cpp

@@ -1219,7 +1219,7 @@ void CMomentaryRotButton::UpdateSelfReturn(float value)
 // Spark
 //----------------------------------------------------------------
 
-class CEnvSpark : public CBaseEntity
+class CEnvSpark : public CPointEntity
 {
 public:
 	void Spawn() override;