add some guards to the completions template

Author: DannyBen

lib/completely/templates/template.erb

@@ -10,7 +10,10 @@
   local result=()
 
   # words the user already typed (excluding the command itself)
-  local used=("${COMP_WORDS[@]:1:$((COMP_CWORD - 1))}")
+  local used=()
+  if ((COMP_CWORD > 1)); then
+    used=("${COMP_WORDS[@]:1:$((COMP_CWORD - 1))}")
+  fi
 
   if [[ "${cur:0:1}" == "-" ]]; then
     # Completing an option: offer everything (including options)
@@ -38,9 +41,14 @@
 
 <%= function_name %>() {
   local cur=${COMP_WORDS[COMP_CWORD]}
-  local compwords=("${COMP_WORDS[@]:1:$COMP_CWORD-1}")
+  local compwords=()
+  if ((COMP_CWORD > 0)); then
+    compwords=("${COMP_WORDS[@]:1:$((COMP_CWORD - 1))}")
+  fi
   local compline="${compwords[*]}"
 
+  COMPREPLY=()
+
 % if ENV['COMPLETELY_DEBUG']
   if [[ -n "$COMPLETELY_DEBUG" ]]; then
     echo "compline: '$compline'" > 'completely-debug.txt'