warn if size of x and y series have different size

Common/onelabUtils.cpp

@@ -262,6 +262,9 @@ namespace onelabUtils {
       for(unsigned int i = 0; i < y.size(); i++) x.push_back(i);
     }
     if(x.size() && y.size()){
+      if(x.size() != y.size())
+        Msg::Warning("X-Y data series have different length (%d != %d)",
+                     (int)x.size(), (int)y.size());
       if(view){
         view->getData()->setXY(x, y);
         view->getData()->setName(yName);