X13: fix option check

Detected by MATLAB Code Analyzer app.

src/utilities/x13/checkoptioncompatibility.m

@@ -22,7 +22,7 @@ if ~isempty(o.estimate.file)
         error('Options ARIMA.model and ESTIMATE.file not compatible!');
     elseif ~isempty(o.arima.ar)
         error('Options ARIMA.ar and ESTIMATE.file not compatible!');
-    elseif ~isempty(o.arima.model)
+    elseif ~isempty(o.arima.ma)
         error('Options ARIMA.ma and ESTIMATE.file not compatible!');
     elseif ~isempty(o.regression.user)
         error('Options REGRESSION.user and ESTIMATE.file not compatible!');