fix(mutt): work around "localvar_inherit"

Author: akinomyoga

completions/mutt

@@ -16,6 +16,7 @@ _muttaddr()
 # @output  muttrc filename
 _muttrc()
 {
+    local muttrc=
     # Search COMP_WORDS for '-F muttrc' or '-Fmuttrc' argument
     set -- "${words[@]}"
     while (($# > 0)); do
@@ -32,7 +33,7 @@ _muttrc()
         shift
     done
 
-    if [[ ! -v muttrc ]]; then
+    if [[ ! $muttrc ]]; then
         if [[ -f ~/.${muttcmd}rc ]]; then
             muttrc=\~/.${muttcmd}rc
         elif [[ -f ~/.${muttcmd}/${muttcmd}rc ]]; then