security: Fix comparison for virSecuritySELinuxRecallLabel

The @con type security_context_t is actually a "char *", so the
correct check should be to dereference one more level; otherwise,
we could return/use the NULL pointer later in a subsequent
virSecuritySELinuxSetFileconImpl call (using @fcon).
Suggested-by: NMichal Prívozník <mprivozn@redhat.com>
Signed-off-by: NJohn Ferlan <jferlan@redhat.com>
Reviewed-by: NJán Tomko <jtomko@redhat.com>

src/security/security_selinux.c

@@ -211,7 +211,7 @@ virSecuritySELinuxRecallLabel(const char *path,
                                       path, con) < 0)
         return -1;
 
-    if (!con)
+    if (!*con)
         return 1;
 
     return 0;