fix GAMESTATE:SetCurrentSteps

assert was causing crash if steps were set to nil/null.

src/GameState.cpp

@@ -2269,7 +2269,7 @@ public:
 		PlayerNumber pn = Enum::Check<PlayerNumber>(L, 1);
 		if( lua_isnil(L,2) )	{ p->m_pCurSteps[pn].Set( NULL ); }
 		else					{ Steps *pS = Luna<Steps>::check(L,2); p->m_pCurSteps[pn].Set( pS ); }
-		ASSERT(p->m_pCurSteps[pn]->m_StepsType == p->m_pCurStyle->m_StepsType);
+		ASSERT( p->m_pCurSteps[pn] == NULL || p->m_pCurSteps[pn]->m_StepsType == p->m_pCurStyle->m_StepsType);
 		return 0;
 	}
 	static int GetCurrentCourse( T* p, lua_State *L )		{ if(p->m_pCurCourse) p->m_pCurCourse->PushSelf(L); else lua_pushnil(L); return 1; }