Don't crash if there is no HandleCheats function in lua.

src/stratagus/stratagus.cpp

@@ -976,7 +976,7 @@ global int main(int argc, char** argv)
 #ifdef USE_WIN32
 	strcpy(LocalPlayerName, "Anonymous");
 #else
-	if (getenv("USERNAME")) {
+	if (getenv("USER")) {
 		strncpy(LocalPlayerName, getenv("USERNAME"), 14);
 	} else {
 		strcpy(LocalPlayerName, "Anonymous");

src/ui/interface.cpp

@@ -996,6 +996,10 @@ global int HandleCheats(const char* input)
 #endif
 	lua_pushstring(Lua, "HandleCheats");
 	lua_gettable(Lua, LUA_GLOBALSINDEX);
+	if (!lua_isfunction(Lua, -1)) {
+		DebugLevel0Fn("No HandleCheats function in lua.\n");
+		return 0;
+	}
 	lua_pushstring(Lua, input);
 	LuaCall(1, 0);
 	ret = lua_gettop(Lua);