PSR12.Files.DeclareStatement - bow out when parse error detected

[fredden]

Description

This began as part of #289.

When a parse error is present, the PSR12.Files.DeclareStatement sniff was incorrectly performing an auto-fix. (That change was then conflicting with PSR12.Operators.OperatorSpacing - #289 includes improvements to that sniff to avoid the conflict from the other end too.) This pull request adds some defensive coding to identify and bow out when a particular parse error is detected. Further defensive coding can be added in future to detect other errors here. (@jrfnl has expressed intention to rewrite this sniff, so I'm not addressing all parse error cases right now.)

Suggested changelog entry

PSR12.Files.DeclareStatement - bow out when parse error detected

Types of changes

• Bug fix (non-breaking change which fixes an issue)

PR checklist

• I have checked there is no other PR open for the same change.
• I have read the Contribution Guidelines.
• I grant the project the right to include and distribute the code under the BSD-3-Clause license (and I have the right to grant these rights).
• I have added tests to cover my changes.
• I have verified that the code complies with the projects coding standards.

[jrfnl]

Related to #152

[jrfnl]

Thanks @fredden !

I'll merge this and will try and get back to the rewrite of the sniff soonish to address everything else ;-)