Merge pull request #5878 from 3dcl/promiseError-undefined

removed invalid .then call using lib.promiseError which does not exis…

Author: archmoj

Diff for: draftlogs/5878_fix.md

@@ -0,0 +1,2 @@
+ - Fix invalid call to `lib.promiseError` in lib.syncOrAsync  [[#5878](https://github.com/plotly/plotly.js/pull/5878)], 
+   with thanks to @jklimke for the contribution!

Diff for: src/lib/index.js

@@ -455,8 +455,7 @@ lib.syncOrAsync = function(sequence, arg, finalStep) {
         ret = fni(arg);
 
         if(ret && ret.then) {
-            return ret.then(continueAsync)
-                .then(undefined, lib.promiseError);
+            return ret.then(continueAsync);
         }
     }