display_iterate: Process only enabled event masks

(krh: Added warning for this unintended usage)
diff --git a/wayland/wayland-client.c b/wayland/wayland-client.c
index 0259017..7bb6451 100644
--- a/wayland/wayland-client.c
+++ b/wayland/wayland-client.c
@@ -494,6 +494,13 @@
 	uint32_t p[2], object, opcode, size;
 	int len;
 
+	mask &= display->mask;
+	if (mask == 0) {
+		fprintf(stderr,
+			"wl_display_iterate called with unsolicited flags");
+		return;
+	}
+
 	len = wl_connection_data(display->connection, mask);
 	while (len > 0) {
 		if (len < sizeof p)