Uninitialized pointer read in ipa-enrollment

This patch fixes a situation where an uninitialized pointer
is passed to free().

https://fedorahosted.org/freeipa/ticket/713

daemons/ipa-slapi-plugins/ipa-enrollment/ipa_enrollment.c

@@ -141,7 +141,7 @@ ipa_join(Slapi_PBlock *pb)
     char * filter;
 
     int scope = LDAP_SCOPE_SUBTREE;
-    char *principal;
+    char *principal = NULL;
     struct berval retbval;
 
     /* Get Bind DN */