4944 Impossible to remove all plugins from the right list of wizard s…

[gitcontributor]

…tep n2 while editing an existing contexts (it seems to happen only in geOrchestra MS project).

Description

Impossible to remove all plugins from the rigth list of wizard step n2 while editing an existing contexts (it seems to happen only in geOrchestra MS project).

Please check if the PR fulfills these requirements

• The commit message follows our guidelines: https://github.com/geosolutions-it/MapStore2/blob/master/CONTRIBUTING.md
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

What kind of change does this PR introduce? (check one with "x", remove the others)

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Other... Please describe:

Issue

What is the current behavior?
#4944

What is the new behavior?
It is now possible to remove all plugins from the rigth list of wizard step n2 while editing an existing ncontexts (it seems to happen only in geOrchestra MS project).

Breaking change

Does this PR introduce a breaking change? (check one with "x", remove the other)

• Yes, and I documented them in migration notes
• No

Other useful information

[coveralls]

Coverage decreased (-0.003%) to 83.843% when pulling 686ea5f on gitcontributor:4944-impossible-remove-all-plugins-contexts into 8fd79e8 on geosolutions-it:master.

[offtherailz]

Please write a unit test that prevents this use case