Fix uninitialized variable used.

Firmware/ultralcd.cpp

@@ -6802,8 +6802,7 @@ bool lcd_selftest()
 		_result = lcd_selftest_manual_fan_check(1, false);
 		if (!_result)
 		{			
-			const char *_err;
-			lcd_selftest_error(6, _err, _err); //print fan not spinning
+			lcd_selftest_error(6, 0, 0); //print fan not spinning
 		}
 
 #endif //defined(TACH_1)