pmprogl_overwrite_confirmation_url doesn't consider pending orders

[dparker1005]

Describe the bug
When purchasing a gift, we redirect users to the invoice page after checkout using the pmprogl_overwrite_confirmation_url method; however, this does not work if the new invoice is in pending status instead of success.

To Reproduce

1. Activate Gift Levels and Pay By Check
2. Purchase a gift level using a check payment
3. See that checkout does not redirect to the invoice page for the newly generated pending invoice.

Isolating the problem (mark completed items with an [x]):

• I have deactivated other plugins and confirmed this bug occurs when only Paid Memberships Pro plugin is active.
• This bug happens with a default WordPress theme active, or Memberlite.
• I can reproduce this bug consistently using the steps above.

WordPress Environment

``` Please share non-sensitive information about your hosting environment such as WordPress version, PHP version, Paid Memberships Pro and any related plugins versions. ```

[kimcoleman]

I'm looking at possible hooks to use - maybe? https://github.com/strangerstudios/paid-memberships-pro/blob/dev/preheaders/checkout.php#L553-L554