QtSingleApplication: Don't hang if client does not send data

Do not wait forever when trying to read data from a connection. The
client might already have been giving up, and the socket therefore
become invalid without any data arriving.

Task-number: QTCREATORBUG-6467
Change-Id: Ie2e52709c92c25539491315bb5106b653df3fe8e
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>