Ext2FS: Block #0 can terminate an inode block list early.

We were already handling this for the indirect blocks, but the direct ones
would happily consider #0 to be a valid block list entry.

Kernel/FileSystem/Ext2FileSystem.cpp

@@ -269,6 +269,11 @@ Vector<Ext2FS::BlockIndex> Ext2FS::block_list_for_inode(const ext2_inode& e2inod
 
  // NOTE: i_blocks is number of 512-byte blocks, not number of fs-blocks.
  unsigned block_count = e2inode.i_blocks / (block_size() / 512);
+
+#ifdef EXT2_DEBUG
+ dbgprintf("Ext2FS::block_list_for_inode(): i_size=%u, i_blocks=%u, block_count=%u\n", e2inode.i_size, block_count);
+#endif
+
  unsigned blocks_remaining = block_count;
  Vector<BlockIndex> list;
  if (include_block_list_blocks) {
@@ -280,7 +285,10 @@ Vector<Ext2FS::BlockIndex> Ext2FS::block_list_for_inode(const ext2_inode& e2inod
 
  unsigned direct_count = min(block_count, (unsigned)EXT2_NDIR_BLOCKS);
  for (unsigned i = 0; i < direct_count; ++i) {
- list.unchecked_append(e2inode.i_block[i]);
+ auto block_index = e2inode.i_block[i];
+ if (!block_index)
+ return list;
+ list.unchecked_append(block_index);
  --blocks_remaining;
  }