changing mapbox icon angle default to 0 + minor code edit

Author: zouhairm

src/traces/scattermapbox/attributes.js

@@ -89,7 +89,7 @@ module.exports = overrideAll({
         },
         angle: {
             valType: 'number',
-            dflt: null,
+            dflt: 0,
             role: 'style',
             arrayOk: true,
             description: [

src/traces/scattermapbox/convert.js

@@ -115,11 +115,7 @@ module.exports = function convert(gd, calcTrace) {
                 });
             }
 
-            if('allowoverlap' in trace.marker) {
-                Lib.extendFlat(symbol.layout,
-                {'icon-allow-overlap': trace.marker.allowoverlap});
-            }
-
+            symbol.layout['icon-allow-overlap'] = trace.marker.allowoverlap;
 
             Lib.extendFlat(symbol.paint, {
                 'icon-opacity': trace.opacity * trace.marker.opacity,