esx: Fix a potential crash

Initialize ptr data.datastorePathWithoutFileName as NULL, otherwise
it might cause crash when trying to free it in cleanup.

src/esx/esx_driver.c

@@ -2698,6 +2698,7 @@ esxDomainGetXMLDesc(virDomainPtr domain, unsigned int flags)
     char *vmx = NULL;
     virVMXContext ctx;
     esxVMX_Data data;
+    data.datastorePathWithoutFileName = NULL;
     virDomainDefPtr def = NULL;
     char *xml = NULL;