fix: change clipboard content when content is really in NetworkPacket
Summary
Clipboard content of desktop is sent to phone when reconnecting after disabling clipboard autoshare. In !661 kdeconnect-kde (not merged), this bug is solved by sending connecting packet without content if autoshare is disabled. If patch 661 merged, KDE Connect Android will read "" (because if no key in NetworkPacket, the default value will be set to "") from connecting packet, and change the clipboard to "". In this patch, if there is no content of connecting packet, do not change clipboard.
BUG: 476551