isConnected not handling waitForACKResponse correctly

[matthewgkerr]

isConnected is assuming sendCommand is returning zero for error, and non-zero for ok. However waitForACKResponse will return SFE_UBLOX_STATUS_DATA_SENT if the response was received, otherwise it could return some other zero or non-zero value. I think isConnected should be checking the return value of sendCommand for SFE_UBLOX_STATUS_DATA_SENT and return true, otherwise return false.

[matthewgkerr]

Looks like this is being addressed in pull request Added better packet validity checking #65.