Don't cleanup distfiles if distfiles is a symlink

It might be a symlink to the master distfiles mirror and we don't want
to risk deleting that.

mpbb-cleanup

@@ -38,10 +38,12 @@ cleanup() {
     # $thisdir is set by mpbb and points to the directory in which this script resides
     # shellcheck disable=SC2154
     "${option_prefix}/bin/port-tclsh" "${thisdir}/tools/uninstall-old-ports.tcl"
-    echo
-    echo "----> Deleting distfiles"
-    find "${option_prefix}/var/macports/distfiles" -type f -mtime +1 -print -delete | sed -E 's/^/Deleting distfile /'
-    find "${option_prefix}/var/macports/distfiles" -type d -mindepth 1 -empty -print -delete | sed -E 's/^/Deleting directory /'
+    if [ ! -L "${option_prefix}/var/macports/distfiles" ]; then
+        echo
+        echo "----> Deleting distfiles"
+        find "${option_prefix}/var/macports/distfiles" -type f -mtime +1 -print -delete | sed -E 's/^/Deleting distfile /'
+        find "${option_prefix}/var/macports/distfiles" -type d -mindepth 1 -empty -print -delete | sed -E 's/^/Deleting directory /'
+    fi
     echo
     for dir in build logs; do
         echo "----> Deleting ${dir}"