Create Issue(s) post-function: throw an error if Summary is not on the Create screen

In the Create Issue(s) post-function, if the Summary field is not on the Create screen of the issue to create, the issue creation will always fail because Summary is always required. We should display an explicit error message instead of the default error message Jra returns in that case, which doesn't point to the root cause (the field not being on the Create screen).