Null ptr check missing from local strdup

[JanneKiiskila]

The implementation of local strdup is not checking for ret being NULL.

https://github.com/WigWagCo/greaseLog/blob/master/local_strdup.c#L25-L26

Standard seems to specify that with invalid values (such as NULL) the behaviour is undefined, which in most cases means a crash. Which is made sure by this line:

	*(ret+n) = '\0';

That pretty much guarantees a memory overwrite to user space address 0+n.

[edhemphill]

Thanks Janne - i'll fix this in https://github.com/WigWagCo/greaseLib - which is the new version of this code. This is basically deprecated.

[JanneKiiskila]

PR created - #5
Is there a CI that tests this? Is the overlaying upper system capable of dealing with NULLPTR? @edhemphill @x85446

[JanneKiiskila]

Seems that this repo is the active one anyway, the link points to a repo that's been archived.