Only prepend {CRYPT} scheme if there is no scheme present

mail-server/dovecot.nix

@@ -65,6 +65,13 @@ let
         # Prevent world-readable password files, even temporarily.
         umask 077
 
+        prepend_scheme() {
+          case "$1" in
+            {*}*) printf '%s' "$1" ;;
+            *) printf '{CRYPT}%s' "$1" ;;
+          esac
+        }
+
         for f in ${
           builtins.toString (lib.mapAttrsToList (name: _: passwordFiles."${name}") cfg.accounts)
         }; do
@@ -81,7 +88,7 @@ let
             if lib.elem name accountsWithPlaintextPasswordFiles then
               "${name}:${"$(sed -n '1{p;p;q}' ${passwordFiles."${name}"} | ${lib.getExe' config.services.dovecot2.package "doveadm"} pw)"}::::::"
             else
-              "${name}:{CRYPT}${"$(head -n 1 ${passwordFiles."${name}"})"}::::::"
+              "${name}:${"$(prepend_scheme \"$(head -n 1 ${passwordFiles."${name}"})\")"}::::::"
           ) cfg.accounts
         )}
         EOF