Avoid call of “Xfree(NULL)”

[elfring]

👀 I find an implementation detail (like the following) suspicious.

libva/va/x11/va_dri2.c

Lines 194 to 195 in e4dc66b

	if (*deviceName == NULL) {
	Xfree(*driverName);

How do you think about to avoid passing null pointers to resource release functions? 🤔