shared IO_CACHE: protection against remove_io_share in a wrong time

bug#3134


BitKeeper/deleted/.del-post-incoming~9f2168f531f09f3b:
  Delete: BitKeeper/triggers/post-incoming
BitKeeper/deleted/.del-post-outgoing~1dd3d8f0f6e8f3cd:
  Delete: BitKeeper/triggers/post-outgoing

BitKeeper/triggers/post-incoming

-#! /bin/sh
-
-echo "Test: post-incoming works"

BitKeeper/triggers/post-outgoing

-#! /bin/sh
-
-echo "Test: post-outgoing works"

mysys/mf_iocache.c

@@ -481,7 +481,8 @@ static int lock_io_cache(IO_CACHE *info, my_off_t pos)
   while (!s->active || s->active->pos_in_file < pos)
     pthread_cond_wait(&s->cond, &s->mutex);
 
-  if (s->total < total)
+  if (s->total < total &&
+      (!s->active || s->active->pos_in_file < pos))
     return 1;
 
   pthread_mutex_unlock(&s->mutex);