luci-proto-wireguard: verify last base64 string symbol is an = sign

Signed-off-by: Florian Eckert <fe@dev.tdt.de>

protocols/luci-proto-wireguard/htdocs/luci-static/resources/protocol/wireguard.js

@@ -10,6 +10,9 @@ function validateBase64(section_id, value) {
 	if (value.length != 44 || !value.match(/^(?:[A-Za-z0-9+\/]{4})*(?:[A-Za-z0-9+\/]{2}==|[A-Za-z0-9+\/]{3}=)?$/))
 		return _('Invalid Base64 key string');
 
+	if (value[43] != "=" )
+		return _('Invalid Base64 key string');
+
 	return true;
 }