push trace module into fullLayout._modules even if visible:false

- so that gl-based trace can call their plot methods w/ an
  empty array of traces and just work.
- this makes restyle(gd, 'visible', false) work properly for
  scattergl traces

Author: etpinard

src/plots/plots.js

@@ -696,7 +696,7 @@ plots._hasPlotType = function(category) {
         if(basePlotModules[i].name === category) return true;
     }
 
-    // check trace modules
+    // check trace modules (including non-visible:true)
     var modules = this._modules || [];
     for(i = 0; i < modules.length; i++) {
         var name = modules[i].name;
@@ -912,7 +912,7 @@ plots.supplyDataDefaults = function(dataIn, dataOut, layout, fullLayout) {
         var _module = fullTrace._module;
         if(!_module) return;
 
-        if(fullTrace.visible === true) Lib.pushUnique(modules, _module);
+        Lib.pushUnique(modules, _module);
         Lib.pushUnique(basePlotModules, fullTrace._module.basePlotModule);
 
         cnt++;