FIXED: JIT clause indexing could mis the right argument in the following scenario:
FIXED: JIT clause indexing could mis the right argument in the following
scenario:

  - There is a best index Ib, which is poor.
  - There is a normally better index I2, but the corresponding
    argument is not indexable.

Although the scenario is not that common, it can lead to a huge
slowdown.  Found by Jos de Roo.

jn7163/swipl-devel,koryonik/swipl-devel,edechter/swipl-devel,koryonik/swipl-devel,jn7163/swipl-devel,mndrix/swipl-devel,edechter/swipl-devel,edechter/swipl-devel,mndrix/swipl-devel,jn7163/swipl-devel,jn7163/swipl-devel,mndrix/swipl-devel,mndrix/swipl-devel,jn7163/swipl-devel,koryonik/swipl-devel,edechter/swipl-devel,mndrix/swipl-devel,koryonik/swipl-devel,koryonik/swipl-devel,edechter/swipl-devel