Use unpack() rather than unpack_from().
Use unpack() rather than unpack_from().

We should be using all the data in the unpack, and using unpack() will
check this.

ahill818/MetPy,jrleeman/MetPy,ahaberlie/MetPy,jrleeman/MetPy,deeplycloudy/MetPy,Unidata/MetPy,Unidata/MetPy,ShawnMurd/MetPy,dopplershift/MetPy,ahaberlie/MetPy,dopplershift/MetPy