Do not close m_socket in socketError()

Summary:
When android closes the payload socket (cancel share) calling m_socket.close() results
in a recursive call to onError eventually leading to a segmentation violation

Test Plan:
Install D16491, share a large file from desktop to android and cancel the share on Android through
the notification. kdeconnectd crashes almost 100% of the time. (It doesn't crash when it detects
a disconnect in sendNextPacket)

Reviewers: KDE Connect, nicolasfella

Reviewed By: KDE Connect, nicolasfella

Subscribers: kdeconnect

Tags: KDE Connect

Differential Revision: https://phabricator.kde.org/D17628