Normally zsh arrays start at index 1 but when emulating other shells
this may change.  During completion, we run the command
  emulate -L sh
which affects the indexing of zsh arrays to make it start at 0.

Consequently, when replacing FUNCNAME by funcstack, we should not
change the index.
Signed-off-by: Marc Khouzam <marc.khouzam@ville.montreal.qc.ca>