Blank parameters are not passed into `next` field in results

[MattHardcastle]

Checklist

• I have verified that that issue exists against the master branch of Django REST framework.
• I have searched for similar issues in both open and closed tickets and cannot find a duplicate.
• This is not a usage question. (Those should be directed to the discussion group instead.)
• This cannot be dealt with as a third party library. (We prefer new functionality to be in the form of third party libraries where possible.)
• I have reduced the issue to the simplest possible case.
• I have included a failing test as a pull request. (If you are unable to do so we can still accept the issue.)

Steps to reproduce

Visit a paginated API using blank URL parameter. For example: http://example.com/api/foo/?bar

Expected behavior

The next link in the results meta data should preserve the blank parameter. Example:

{
    "next": "http://example.com/api/foo/?bar&page=2",
   ...
}

Actual behavior

The next link in the results meta data swallows the blank parameter. Example:

{
    "next": "http://example.com/api/foo/?page=2",
   ...
}

I have an open pull request with a tests for this case.

[lovelydinosaur]

Closed via #4260.