Deleting the last plan of a level doesn't get deleted

[JarrydLong]

Describe the bug

Creating a single plan on a level, saving the level and then deciding to remove it results in the level not being removed after saving the level.

To Reproduce
Steps to reproduce the behavior:

1. Edit your level and add one payment plan to it. Save the level.
2. Edit the same level, remove the plan and save the level
3. Edit the level again, the plan will still show in the level settings.

Screenshots

Expected behavior
Removing a plan should be removed accordingly after saving a level

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

Details

PMPro 3.5.3 Payment Plans Add On 0.5