Fix - verify that TH1/TH2 superimposing in 3D works properly

If first histogram (which defines axes and 3D mode) drawn in 2D, of
course second histograms cannot be drawn in 3D. Provide simple check to
prevent civiar errors

Author: linev

scripts/JSRootPainter.hist3d.js

@@ -1523,13 +1523,12 @@
             main.DrawXYZ(main.toplevel, { use_y_for_z: true, zmult: 1.1, zoom: JSROOT.gStyle.Zooming, ndim: 1 });
          }
 
-         this.Draw3DBins();
-
-         main.Render3D();
-
-         this.UpdateStatWebCanvas();
-
-         main.AddKeysHandler();
+         if (main.mode3d) {
+            this.Draw3DBins();
+            main.Render3D();
+            this.UpdateStatWebCanvas();
+            main.AddKeysHandler();
+         }
       }
 
       if (is_main) {
@@ -1580,13 +1579,12 @@
             main.DrawXYZ(main.toplevel, { zmult: zmult, zoom: JSROOT.gStyle.Zooming, ndim: 2 });
          }
 
-         this.Draw3DBins();
-
-         main.Render3D();
-
-         this.UpdateStatWebCanvas();
-
-         main.AddKeysHandler();
+         if (main.mode3d) {
+            this.Draw3DBins();
+            main.Render3D();
+            this.UpdateStatWebCanvas();
+            main.AddKeysHandler();
+         }
       }
 
       if (is_main) {