fix #5031 for false error when deleting plugin DB field

[Jimmi08]

Motivation and Context

Fixes #5031

How Has This Been Tested?

with real example

		<field name="uid" type='EUF_DB_FIELD' text="UID" default='0' active="true" system="0" parms="plugin_efiction^,^^,^^,^0^,^^,^" 
			values="fanfiction_authors,uid,penname,penname" read="250" write="250" applicable="253" required="0" />

Types of Changes

• [x ] Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Performance enhancement (non-breaking change which improves efficiency)
• Code cleanup (non-breaking change which makes code smaller or more readable)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation (a change to man pages or other documentation)

Checklist

• My code adheres to the e107 code style standard.
• I have read the contributing document.
• I have added tests to cover my changes.
• All new and existing tests pass.