Fix fetching all issues when maxResults is Falsy

[georgyo]

There are two problems that are currently affecting the ability to
fetch all results.

1. In older versions of this code when maxResults was falsy, it would
   then change it to be 50, and then iterate over the code. This was
   changed to a much more ideal method, however the old code blindly put
   the value of maxResults into the dict of search params. It didn't matter
   as it get reassigned pretty fast. The new code still put's it blindly
   into the map, but then never reassigns it, and continues to do a search
   with it to determin how many results there are. Which creates an invalid
   search query. Solution: Remove it from being added to the map. It
   actually never intentionally used in that map without having it
   reassigned first.

2. There is this isLast code, which likely could be removed entirely.
   It, according to the comment only works with the Jira agile module. If
   jira doesn't know what isLast is, the code would return that is_last is
   True. Obviously this is a bad failure case, as if we don't have the
   agile module we can only ever return one page. Solution: Change the
   default to False.

[review-ninja]

[georgyo]

This fixes #229, #253, and #269 by actually fixing the problems and not breaking compatibility with older releases. The other solutions to this problem didn't even seem to look at the code.

@olivierlefloch Pinging you, since you have tried to fix these issues before.

[atulatri]

+1

[ssbarnea]

Closing because this seems to make maxResults parameter not functional. Still, is this in not yet solved I would recommend writing a small unittest for testing this bug.