Reset the Background Queue after Dispatch

[jakejackson1]

Description

This fixes an issue when creating multiple entries via the GFAPI, whereby the queue was not empty before each new entry was processed. The more entries added in a single request, the more duplicate notifications were sent.

Testing instructions

1. Enable PDF Notifications on a test form and PDF Background Processing in the settings
2. Generate multiple entries on demand using code like this:

add_action('admin_init', function() {
    if( empty( $_GET['test1'] ) ) {
        return;
    }

    $backup_post = $_POST;

    for ( $i = 0; $i < 3; $i ++ ) {
        $entry = [
            'input_1' => 'test' . rand(),
            'input_3' => 'test' . rand(),
            'input_4' => 'test' . rand(),
        ];

        $results = \GFAPI::submit_form( 848, $entry );

        $_POST = $backup_post;
        \GFFormsModel::flush_current_lead();
        \GFFormDisplay::$submission = [];
    }
} );

3. Verify you only get 3 emails with a PDF attached to each.

Screenshots

Checklist:

• [x] I've tested the code.
• [x] My code is easy to read, follow, and understand
• [ ] My code follows the accessibility standards.
• [x] My code has proper inline documentation / docblocks.

Additional Comments

[codecov[bot]]

Codecov Report

Merging #1446 (5390a53) into development (60824d2) will increase coverage by 17.59%. The diff coverage is n/a.

@@                Coverage Diff                 @@
##             development    #1446       +/-   ##
==================================================
+ Coverage          75.70%   93.30%   +17.59%     
==================================================
  Files                243       57      -186     
  Lines              12827     1464    -11363     
  Branches             370      370               
==================================================
- Hits                9711     1366     -8345     
+ Misses              3108       90     -3018     
  Partials               8        8               

Impacted Files	Coverage Δ
src/Controller/Controller_Pdf_Queue.php
src/Helper/Helper_Field_Container_Void.php
src/View/html/Settings/tabs.php
src/Helper/Fields/Field_Multiselect.php
src/Helper/Helper_Abstract_Fields.php
src/templates/rubix.php
src/Helper/Fonts/TtfFontValidation.php
src/Model/Model_Actions.php
src/autoload.php
src/Helper/Fields/Field_Tos.php
... and 176 more

Help us with your feedback. Take ten seconds to tell us how you rate us. Have a feature suggestion? Share it here.