qemu: Don't crash when create fails early

Since commit 7140807917 we are generating
socket path later than before -- when starting a domain.  That makes one
particular inconsistent state of a chardev, which was not possible
before, currently valid.  However, SELinux security driver forgot to
guard the main restoring function by a check for NULL-paths.  So make it
no-op for NULL paths, as in the DAC driver.

Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1300532

Signed-off-by: Martin Kletzander <mkletzan@redhat.com>

src/security/security_selinux.c

@@ -1024,6 +1024,12 @@ virSecuritySELinuxRestoreFileLabel(virSecurityManagerPtr mgr,
     char *newpath = NULL;
     char ebuf[1024];
 
+    /* Some paths are auto-generated, so let's be safe here and do
+     * nothing if nothing is needed.
+     */
+    if (!path)
+        return 0;
+
     VIR_INFO("Restoring SELinux context on '%s'", path);
 
     if (virFileResolveLink(path, &newpath) < 0) {