Handle specially if no time about the last index update found.

The explorer 'currage' now returns -1 if he can not find any value about
this. The gencode-remote script handle this value special to not exit if
-1 given as value.

This fixes the bug
  ungleich-public/cdist#803

cdist/conf/type/__package_update_index/explorer/currage

@@ -24,18 +24,18 @@ case "$type" in
         if [ -f "/var/cache/apt/pkgcache.bin" ]; then
             echo $(($(date +"%s")-$(stat --format '%Y' /var/cache/apt/pkgcache.bin)))
         else
-            echo 0
+            echo -1
         fi
         ;;
     pacman)
         if [ -d "/var/lib/pacman/sync" ]; then
             echo $(($(date +"%s")-$(stat --format '%Y' /var/lib/pacman/sync)))
         else
-            echo 0
+            echo -1
         fi
         ;;
     alpine)
-        echo 0
+        echo -1
         ;;
     *)  echo "Your specified type ($type) is currently not supported." >&2
         echo "Please contribute an implementation for it if you can." >&2

cdist/conf/type/__package_update_index/gencode-remote

@@ -31,7 +31,8 @@ if [ -n "$maxage" ]; then
     if [ "$type" != "apt" ] && [ "$type" != "pacman" ]; then
         echo "ERROR: \"--maxage\" only supported for \"apt\" or \"pacman\" pkg-manager." >&2
         exit 1
-    elif [ "$currage" -lt "$maxage" ]; then
+    # do not exit if no value found (represented as -1)
+    elif [ "$currage" -ne -1 ] && [ "$currage" -lt "$maxage" ]; then
         exit 0 # no need to update
     fi
 fi