Adding Update Issue Field workflow postfunction causes OutOfMemoryError

Problem Description:

assignee dropdown on workflow postfunction can expend the heap on large installations

An application fatal heap overflow occurs when applying a workflow post-function where the installation has many hundreds of projects and thousands of users. If a post function 'update issue field' is selected, (or possibly other functions which involve dropdown fields rather than user pickers) the rendered html source will include inline all dropdown options - eg. 600 projects x 1,000 users who are assignable to that project. This calculation loop can expend available memory and cause general system slowdown.

Specifically this happens when adding an 'Update Issue Field' post function in a workflow. The "Assign to User" field tries to build a list of all assignable users, however in this case there is no project context so it builds up a list of assignable users per project. If a user is assignable in multiple projects, they appear in the list multiple times.

Recommendation: Change the dropdown to a user picker.