core/device: Don't even attempt to load name if address is private

Device with private address does not have their name stored so it makes
not sense to attempt to load their names.
diff --git a/src/device.c b/src/device.c
index 83a794e..5506bc9 100644
--- a/src/device.c
+++ b/src/device.c
@@ -2655,6 +2655,9 @@
 	char *str = NULL;
 	int len;
 
+	if (device_address_is_private(device))
+		return NULL;
+
 	snprintf(filename, PATH_MAX, STORAGEDIR "/%s/cache/%s", local, peer);
 
 	key_file = g_key_file_new();