Merge branch 'fix-plot-crash' into 'master'

Avoid crash when plot area hasn't been initialized yet

See merge request aroffringa/aoflagger!127

plot/heatmap.cpp

@@ -507,17 +507,19 @@ void HeatMap::postRender(const Cairo::RefPtr<Cairo::Context>& cairo,
   const Rectangle pArea = getPlotArea(width, height);
   const double xAxisSize = _xAxisMax - _xAxisMin;
   const double yAxisSize = _yAxisMax - _yAxisMin;
-  cairo->save();
-  cairo->transform(Cairo::Matrix(pArea.width / xAxisSize, 0.0, 0.0,
-                                 -pArea.height / yAxisSize,
-                                 pArea.x - _xAxisMin * pArea.width / xAxisSize,
-                                 height - (height - pArea.height - pArea.y) +
-                                     _yAxisMin * pArea.height / yAxisSize));
-  // cairo->rectangle(0.0, 0.0, xAxisSize, yAxisSize);
-  // cairo->clip();
-
-  _signalDraw(cairo);
-  cairo->restore();
+  if (xAxisSize != 0.0 && yAxisSize != 0.0) {
+    cairo->save();
+    cairo->transform(Cairo::Matrix(
+        pArea.width / xAxisSize, 0.0, 0.0, -pArea.height / yAxisSize,
+        pArea.x - _xAxisMin * pArea.width / xAxisSize,
+        height - (height - pArea.height - pArea.y) +
+            _yAxisMin * pArea.height / yAxisSize));
+    // cairo->rectangle(0.0, 0.0, xAxisSize, yAxisSize);
+    // cairo->clip();
+
+    _signalDraw(cairo);
+    cairo->restore();
+  }
 }
 
 void HeatMap::findMinMax(const ImageInterface& image, float& min, float& max) {