Provide a valid default port when parsing QUrl

When port is not specified in QUrl, the default value is
returned. This default value is -1, which was promptly cast to an
unsigned integer.
Allocate internal structures before using them

ClientPrivate::parseCnnString() touches class parameters that are
allocated in the init() function.
Merge pull request #39 from AdamMajer/master

This fixes segfaults trying to use the QAMQP::Client constructor with passed QUrl