define variable (gives compiler warning otherwise) and avoid zero division

modules/gui/src/data_viewer/argand.cc

@@ -103,7 +103,7 @@ void Argand::update_buffer()
   pnt.drawLine(0,p0.y(),size().width(),p0.y());
   if (!has_data_ || GetObservedData().GetType()!=COMPLEX) return;
   
-  Real maxlen;
+  Real maxlen = 0.0;
   std::vector<Complex> data_list;
   for(ExtentIterator it(extent_); !it.AtEnd(); ++it) {
     Complex v = GetObservedData().GetComplex(it);
@@ -113,6 +113,10 @@ void Argand::update_buffer()
     data_list.push_back(v);
   }
 
+  if(maxlen == 0.0) {
+    return;    // return to avoid zero division
+  }
+
   int dim=std::min(size().width(),size().height());
   sf_=0.5*(Real)(dim-10)/maxlen;