Hide 3d plot when bad data

If the model plot cannot be refreshed when data
is invalid, the plot needs to be hidden since the
qwtplot3d api does not redraw empty plots and does
not have any methods for clearing the canvas.

This workaround just hides the plot and shows a label
when the plot is invalidated.

Fixes #429.

src/ModelWindow.cpp

@@ -53,6 +53,10 @@ ModelWindow::ModelWindow(MainWindow *parent, const QDir &home) :
     QFormLayout *cl = new QFormLayout(c);
     setControls(c);
 
+    // hidden text when plot invalid
+    nodata = new QLabel(tr("No data or bin size too large."), this);
+    nodata->hide();
+
     // the plot widget
     QHBoxLayout *mainLayout = new QHBoxLayout;
     modelPlot= new ModelPlot(main, NULL);
@@ -63,6 +67,7 @@ ModelWindow::ModelWindow(MainWindow *parent, const QDir &home) :
     zpane->setValue(0);
     mainLayout->addWidget(zpane);
     mainLayout->addWidget(modelPlot);
+    mainLayout->addWidget(nodata);
     setLayout(mainLayout);
 
     // preset Values
@@ -238,8 +243,24 @@ ModelWindow::setData(bool adjustPlot)
         if (current != NULL && current->isSelected() == true)
                 settings.intervals.append(current);
     }
+
+    setUpdatesEnabled(false);
+
+    // reset the model parameters
     modelPlot->setData(&settings);
+
+    // if setdata resulted in the plot being hidden
+    // then the settings were not valid.
+    if (modelPlot->basicModelPlot->isHidden()) {
+        zpane->hide();
+        nodata->show();
+    } else {
+        zpane->show();
+        nodata->hide();
+    }
     setClean();
+
+    setUpdatesEnabled(true);
 }
 
 void