fix index error in casida mode

- for matrices of even size, half of the rows to be computed have one
  entry less than the other half
- with the previous indexing, some elements are computed twice, others
  remain zero
- with the fix, the full matrix is computed
1 job for fix-casida in 0 seconds
Status Job ID Name Coverage
  External
passed Octopus Buildbot

04:24:32