fscache: fix crash when clearing the cache

fscache_clear was crashing because when using hashmap_iter_next
method the next entry will be saved.  Meanwhile the call to
fscache_release will free the directory and the list of entries
for the directory.  This causes the next entry saved by the iter
to be freed, invalid and the crash with the next loop iteration.

This changes the clear to simple call hashmap_free to free
the hashmap and all the entries and then call hashmap_init to
reinitialize the hashmap for the next fscache use.  The reason
this is safe is fscache_clear is only called from fscache_enable
when this cache is being disabled which is only called in
preload_index after all the thread have exited.
It is also guarded by the critical section mutex.

Author: Kevin Willford

compat/win32/fscache.c

@@ -238,32 +238,13 @@ static void fscache_add(struct fsentry *fse)
 		hashmap_add(&map, fse);
 }
 
-/*
- * Removes a directory listing from the cache.
- */
-static void fscache_remove(struct fsentry *fse)
-{
-	if (fse->list)
-		fse = fse->list;
-
-	for (; fse; fse = fse->next)
-		hashmap_remove(&map, fse, NULL);
-}
-
 /*
  * Clears the cache.
  */
 static void fscache_clear(void)
 {
-	struct hashmap_iter iter;
-	struct fsentry *fse;
-	hashmap_disallow_rehash(&map, 1);
-	hashmap_iter_init(&map, &iter);
-	while ((fse = hashmap_iter_next(&iter))) {
-		fscache_remove(fse);
-		fsentry_release(fse);
-	}
-	hashmap_disallow_rehash(&map, 0);
+	hashmap_free(&map, 1);
+	hashmap_init(&map, (hashmap_cmp_fn)fsentry_cmp, 0);
 }
 
 /*