[xml] Potential NULL pointer dereference in xmlregexp.c

[Shaobo He <polarishehn gmail com>]

Hello everyone,

I'm Shaobo He, a graduate student at University of Utah. I'm running a static analysis tool on libxml2 and noticed there may be a NULL pointer dereference in function `xmlRegexpIsDeterminist`. Basically, function `xmlNewAutomata` can return a NULL pointer when malloc fails. Please let me know if it makes sense or not.

Thanks,

Shaobo