[Bibtex] Error: Call to a member function getLanguage() on null

[hktang]

Please follow the general troubleshooting steps first:

• I read the README and followed the instructions.
• I am sure that the used CSL metadata follows the CSL schema.
• I use a valid CSL stylesheet (bibtex.csl)

Bug reports:

Related to #184 , It seems CiteProc::getContext()->getLocale() is null when using bibtex.csl.

strtok(CiteProc::getContext()->getLocale()->getLanguage(), '-');

Proposal is to supply the default locale "en" if it does not exist, because strtok does not accept null any more.

strtok(CiteProc::getContext()->getLocale()?->getLanguage() ?? "en", '-');