settings/d-bus: fix boolean return value of "LoadConnections"

The boolean value is intended to indicate success. It would indicated
failure due to a bug.

Fixes: 297d4985ab ('core/dbus: rework D-Bus implementation to use lower layer GDBusConnection API'):

src/settings/nm-settings.c

@@ -1460,7 +1460,7 @@ next_filename:
 
 	g_dbus_method_invocation_return_value (invocation,
 	                                       g_variant_new ("(b^as)",
-	                                                      (gboolean) (!!failures),
+	                                                      (gboolean) (!failures),
 	                                                      failures
 	                                                        ? (const char **) failures->pdata
 	                                                        : NM_PTRARRAY_EMPTY (const char *)));