fix(zsh): store exit code first in precmd hook

Addresses an issue causing exit code segments to incorrectly report an
exit code of `0`

src/init/omp.zsh

@@ -5,8 +5,8 @@ function omp_preexec() {
 }
 
 function omp_precmd() {
-  omp_stack_count=${#dirstack[@]}
   omp_last_error=$?
+  omp_stack_count=${#dirstack[@]}
   omp_elapsed=-1
   if [ $omp_start_time ]; then
     omp_now=$(::OMP:: --millis)