Fix FILO-not-having-unmount workaround

We want to reset the state when we already mounted an FS before.

Signed-off-by: Nico Huber <nico.huber@secunet.com>
diff --git a/src/filo-fs-vfs.adb b/src/filo-fs-vfs.adb
index b190bd7..e140b6a 100644
--- a/src/filo-fs-vfs.adb
+++ b/src/filo-fs-vfs.adb
@@ -27,7 +27,7 @@
    is
       Success : Boolean;
    begin
-      if not Is_Mounted (State) then
+      if Is_Mounted (State) then
          State := Initial; -- Work around not having an unmount in FILO.
       end if;
       Mount (State, Part_Len, Success);