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/ModelPlot.cpp

@@ -172,11 +172,10 @@ class ModelDataProvider : public Function
             plot.inum.clear();
         }
 
-    private:
-
         QHash<QString, double> mz;        // xy map with max z values;
         QHash<QString, int> mnum;      // xy map with count of values for averaging
 
+    private:
 
         double pointType(const RideFilePoint *, int);
         QString describeType(int, bool);
@@ -476,9 +475,10 @@ ModelDataProvider::ModelDataProvider (BasicModelPlot &plot, ModelSettings *setti
 
         // create a null plot -- bin too large!
         plot.setTitle("No data or bin size too large");
+        // initialise a null plot
         setDomain(0,0,0,0);
-        setMesh(2,2);
         setMinZ(0);
+        setMesh(0,0);
         mz.clear();
         settings->colorProvider->color.clear();
         create();
@@ -813,6 +813,7 @@ BasicModelPlot::BasicModelPlot(MainWindow *parent, ModelSettings *settings) : ma
     // the data provider returns a z for an x,y
     modelDataProvider = new ModelDataProvider(*this, settings);
 
+
 // qwtplot3d api changes between 0.2.x and 0.3.x
 #if QWT3D_MINOR_VERSION < 3
     setDataColor(modelDataColor);
@@ -926,6 +927,12 @@ BasicModelPlot::setData(ModelSettings *settings)
     delete modelDataProvider;
     settings->colorProvider = modelDataColor;
     modelDataProvider = new ModelDataProvider(*this, settings);
+
+    if (modelDataProvider->mz.count() == 0) {
+        hide();
+    } else {
+        show();
+    }
     //modelDataProvider->assign(this);
     //create();
     //resetViewPoint();