Fix for issue #371

[PlaneNuts]

Checklist before requesting a review

Please delete options that are not relevant.

• I have performed a self-review of my code.
• I have added tests (when available) that prove my fix is effective or that my feature works.
• This change requires a documentation update.

Description

• It fixes Error: SQL Warnings: 1292 #371
• Here is a brief description of what this PR does: When loading the form to add a new injection model the DB is queried multiple times by the checkRightOnModel() function with "" as the $models_id (since no model is being selected). This throws multiple errors of

SQL Warnings: 1292: Truncated incorrect DECIMAL value: '' in query "(SELECT `itemtype` FROM `glpi_plugin_datainjection_models` WHERE `id` = '') UNION (SELECT DISTINCT `itemtype` FROM `glpi_plugin_datainjection_mappings` WHERE `models_id` = '') UNION (SELECT DISTINCT `itemtype` FROM `glpi_plugin_datainjection_infos` WHERE `models_id` = '')"

This change sets it to -1 when null in order to feed a valid value into the query.

I've confirmed that existing models still load without issue, and the error for a new model no longer appears.

Screenshots (if appropriate):

[stonebuzz]

Hi @PlaneNuts

can you adapt CHANGELOG.md ?

Best regards