Fix DD load balancing bug with GPU sharing
The recent DD load balancing fix which solved the issue of incorrect
imbalance measure with GPU sharing (
ba8232e9) addressed GPUs with
incorrect indexing. This caused out of bounds indexing in the GPU ID
query function. The query function also had a bug in the error checking
which allowed the incorrect indexing.
Now also mdrun -nb cpu -gpu_id ... is allowed, which before would give
a fatal error.
This commit addresses both issues; fixes #1385
Change-Id: I2800f610b873da92afe78bbfd869258f378ba2d7