clients: Silence 2x gcc 4.6.3 "warn_unused_result" compiler warnings

window.c:1173:6: warning: ignoring return value of ‘read’, declared with attribute warn_unused_result [-Wunused-result]
desktop-shell.c:305:6: warning: ignoring return value of ‘read’, declared with attribute warn_unused_result [-Wunused-result]
diff --git a/clients/desktop-shell.c b/clients/desktop-shell.c
index 0605f84..fbc0604 100644
--- a/clients/desktop-shell.c
+++ b/clients/desktop-shell.c
@@ -302,7 +302,8 @@
 		container_of(task, struct panel_clock, clock_task);
 	uint64_t exp;
 
-	read(clock->clock_fd, &exp, sizeof exp);
+	if (read(clock->clock_fd, &exp, sizeof exp) != sizeof exp)
+		abort();
 	widget_schedule_redraw(clock->widget);
 }