Fix constant check

[johannescoetzee]

This PR fixes the missing files issue in the vavkamil/dvwp repo. I couldn't find a minimal example to reproduce the issue, but manually verified that the ast is non-empty for these files when using this version of php-parser with joern. Logs are shown for one of the files below, but the other looks the same (apart from numbers)

With the fix

❯ ./joern-cli/frontends/php2cpg/php2cpg --php-parser-bin ~/code/PHP-Parser/bin/php-parse ~/path/to/dvwp/otherz/search-replace-db/srdb.class.php
...
[INFO ] Start of pass: io.joern.php2cpg.passes.AstCreationPass
[INFO ] Pass io.joern.php2cpg.passes.AstCreationPass completed in 580 ms (7% on mutations). 7826 + 0 changes committed from 1 parts.

Without the fix

❯ ./joern-cli/frontends/php2cpg/php2cpg ~/path/to/dvwp/otherz/search-replace-db/srdb.class.php
...
[INFO ] Start of pass: io.joern.php2cpg.passes.AstCreationPass
[INFO ] Pass io.joern.php2cpg.passes.AstCreationPass completed in 102 ms (1% on mutations). 0 + 0 changes committed from 1 parts.

[mpollmeier]

note that the php parser version is configured in both joern and x2cpg-internal (for now), so please update it in both places - thank you!

[johannescoetzee]

Ah, thanks for the heads-up!