formatted apm completion and used helper function

completion/available/apm.completion.bash

@@ -24,7 +24,9 @@
 
 # repo: https://github.com/vigo/apm-bash-completion
 
-__apm(){
+if _command_exists apm
+then
+    function __apm(){
         local cur prev options apm_command
         COMPREPLY=()
         cur="${COMP_WORDS[COMP_CWORD]}"
@@ -50,8 +52,9 @@ __apm(){
             fi
         fi
         COMPREPLY=($(compgen -W "$options" -- "$cur"))
-}
-__apm_get_command() {
+    }
+
+    function __apm_get_command() {
         local i
         for ((i=1; i < $COMP_CWORD; ++i)); do
             local arg=${COMP_WORDS[$i]}
@@ -73,5 +76,7 @@ __apm_get_command() {
                 return;;
             esac
         done
-}
-complete -F __apm -o bashdefault -o default apm
+    }
+
+    complete -F __apm -o bashdefault -o default apm
+fi