Support string $upgrade_link_args in FrmAddonsController::conditional_action_button

[Crabcyborg]

Fixes #1405

The welcome page passes views-info for the upgrade link args. The function was setting an array key, which causes issues when the variable isn't an array.

This update sets it to an array. By the time FrmAppHelper::admin_upgrade_link is called, we no longer need the medium value being passed in $upgrade_link_args. If it's a string, it's fine to set it to an empty array.

The next line sets the link as before, now with an array value.

PHP Fatal error: Uncaught TypeError: Cannot access offset of type string on string in /var/www/src/wp-content/plugins/formidable/classes/controllers/FrmAddonsController.php:1260
Stack trace:
#0 /var/www/src/wp-content/plugins/formidable/classes/controllers/FrmWelcomeController.php(175): FrmAddonsController::conditional_action_button('views', 'views-info')
#1 /var/www/src/wp-content/plugins/formidable/classes/views/welcome/show.php(82): FrmWelcomeController::maybe_show_conditional_action_button('views', 'views-info')
#2 /var/www/src/wp-content/plugins/formidable/classes/controllers/FrmWelcomeController.php(102): include('/var/www/src/wp...')
#3 /var/www/src/wp-includes/class-wp-hook.php(324): FrmWelcomeController::screen_content('')
#4 /var/www/src/wp-includes/class-wp-hook.php(348): WP_Hook->apply_filters('', Array)
#5 /var/www/src/wp-includes/plugin.php(517): WP_Hook->do_action(Array)
#6 /var/www/src/wp-admin/admin.php(259): do_action('forms_page_form...')
#7 {main}

[codecov]

Codecov Report

Attention: 2 lines in your changes are missing coverage. Please review.

Comparison is base (0b78246) 29.12% compared to head (7e2d849) 29.11%.

Files	Patch %	Lines
classes/controllers/FrmAddonsController.php	0.00%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #1406      +/-   ##
============================================
- Coverage     29.12%   29.11%   -0.01%     
- Complexity     7294     7295       +1     
============================================
  Files           105      105              
  Lines         24058    24060       +2     
============================================
  Hits           7006     7006              
- Misses        17052    17054       +2     

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