fix JSON propety validation of inject node

[HiroyasuNishiyama]

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)

Proposed changes

JSON type property value is expected to be validated in inject node. But it do not work correctly.
This is caused by missing variable reference of property type checking.
This PR tries to fix this problem.

Checklist

• I have read the contribution guidelines
• For non-bugfix PRs, I have discussed this change on the forum/slack team.
• I have run grunt to verify the unit tests pass
• I have added suitable unit tests to cover the new/changed functionality

[coveralls]

Coverage remained the same at 67.383% when pulling f786c7f on node-red-hitachi:fix-inject-property-validation into 943b103 on node-red:master.