Fixed bug caused by emptying the modebar div without resetting the modebar state

Author: yook-at-work

src/plot_api/plot_api.js

@@ -3749,6 +3749,7 @@ function makePlotFramework(gd) {
         .classed('main-svg', true);
 
     fullLayout._modebardiv = fullLayout._paperdiv.append('div');
+    delete fullLayout._modeBar;
 
     fullLayout._hoverpaper = fullLayout._paperdiv.append('svg')
         .classed('main-svg', true);