keep ref to subplot image/shape layers in main drawData

- so that these ref on fullLayout exist even for
  non-cartesian trace types.

Author: etpinard

src/plot_api/plot_api.js

@@ -258,6 +258,11 @@ Plotly.plot = function(gd, data, layout, config) {
             basePlotModules[i].plot(gd);
         }
 
+        // keep reference to shape layers in subplots
+        var layerSubplot = fullLayout._paper.selectAll('.layer-subplot');
+        fullLayout._imageSubplotLayer = layerSubplot.selectAll('.imagelayer');
+        fullLayout._shapeSubplotLayer = layerSubplot.selectAll('.shapelayer');
+
         // styling separate from drawing
         Plots.style(gd);
 

src/plots/cartesian/index.js

@@ -178,11 +178,6 @@ function updateSubplots(gd) {
         // so they end up on top of the rest
         plotinfo.draglayer = joinLayer(fullLayout._draggers, 'g', subplot);
     });
-
-    // keep reference to shape layers in subplots
-    var layerSubplot = fullLayout._paper.selectAll('.layer-subplot');
-    fullLayout._imageSubplotLayer = layerSubplot.selectAll('.imagelayer');
-    fullLayout._shapeSubplotLayer = layerSubplot.selectAll('.shapelayer');
 }
 
 function makeSubplotData(gd) {