Fix malformed redirect URLs

[christianwach]

Overview

Fixes Issue 460. Please refer to that for details.

Prevents CRM_Core_QuickForm_Action_Jump::perform() from constructing invalid URLs.

Before

Can produce URLs like this:

https://civicrm.latest/civicrm/event/register/?&_qf_ThankYou_display=true&qfKey=<some-key>

After

Will build URL like this:

https://civicrm.latest/civicrm/event/register/?_qf_ThankYou_display=true&qfKey=<some-key>

[civibot]

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[christianwach]

Related PR: #11708

[kcristiano]

Tested and PR works as described. Further comments:

https://lab.civicrm.org/dev/core/issues/460#note_10049

[kcristiano]

Tested on WP 4.9.8 and CiviCRM master as well as Drupal 7 and CiviCRM Master

• (r-explain) Pass
• (r-test) Pass
• (r-code) Pass
• (r-doc) Pass
• (r-maint) Pass
• (r-run) Pass
• (r-user) Pass
• (r-tech) Pass

The code here fixes the malformed URL and is an improvement. This PR is merge ready.

[seamuslee001]

Adding merge on pass based on @kcristiano testing

[seamuslee001]

Merging as per Kevin's testing