Align NetworkPacket.hasPayload with desktop

Summary:
On desktop NetworkPacket.hasPayload() tests m_payloadSize
On android NetworkPacket.hasPayload() tests mPayload

This patch makes android also test mPayloadSize to make things more consistent

Reviewers: KDE Connect, albertvaka

Reviewed By: KDE Connect, albertvaka

Subscribers: kdeconnect

Tags: KDE Connect

Differential Revision: https://phabricator.kde.org/D17236