perf(bash-v2): read directly to COMPREPLY on descriptionless short circuit (#1700)

Not that it'd really matter that much performancewise given the level we
are at for this case, but this change makes the short circuit roughly
twice as fast on my box as it was for the 1000 rounds done in
marckhouzam/cobra-completion-testing.

Perhaps more importantly, this makes the code arguably slightly cleaner.

bash_completionsV2.go

@@ -178,9 +178,7 @@ __%[1]s_handle_standard_completion_case() {
 
     # Short circuit to optimize if we don't have descriptions
     if [[ $out != *$tab* ]]; then
-        while IFS='' read -r comp; do
-            COMPREPLY+=("$comp")
-        done < <(IFS=$'\n' compgen -W "$out" -- "$cur")
+        IFS=$'\n' read -ra COMPREPLY -d '' < <(IFS=$'\n' compgen -W "$out" -- "$cur")
         return 0
     fi