Handle new INFINITE positions in TRES nodes

In 18.08, the stats are stored in TRES arrays and uses the
slurmdb_find_tres_count_in_string() function to return the TRES value.
If a value doesn't exist, the function returns INFINITE64. But < 18.08
is expecting NO_VAL values.

e.g.
A TRES position of INFINTE caused a lappy0 node to be shown -- I don't
have a lappy0.
brian@lappy:~/slurm/master/lappy$ sacct -j 232809 -o MaxVMSizeNode
 MaxVMSizeNode
--------------

        lappy0