Fix data block length when uncompressing TNG data.

Also, if there are no bonds in a molecule do not reserve
memory for them (to avoid a returned NULL pointer).

Change-Id: I06f9ad71711174017a229faec53d6dca08ee99d0
TNG Fix for GMX_DOUBLE builds and where ZLIB is not available.

Also includes a check that the user name can be retrieved
before trying to set it.

Change-Id: I51d4ab2e590752980953d1926d4bea56fe1beffa