[JFFS2] Handle inodes with only a single metadata node with non-zero isize

This should never happen unless there's corruption on the medium and the
actual data nodes go missing. But the failure mode (an oops when we assume
the fragtree isn't empty and go looking for its last node) isn't useful.

Signed-off-by: David Woodhouse <dwmw2@infradead.org>
diff --git a/fs/jffs2/nodelist.h b/fs/jffs2/nodelist.h
index cb34cac..25126a0 100644
--- a/fs/jffs2/nodelist.h
+++ b/fs/jffs2/nodelist.h
@@ -362,7 +362,7 @@
 struct rb_node *rb_prev(struct rb_node *);
 void rb_replace_node(struct rb_node *victim, struct rb_node *new, struct rb_root *root);
 int jffs2_add_full_dnode_to_inode(struct jffs2_sb_info *c, struct jffs2_inode_info *f, struct jffs2_full_dnode *fn);
-void jffs2_truncate_fragtree (struct jffs2_sb_info *c, struct rb_root *list, uint32_t size);
+uint32_t jffs2_truncate_fragtree (struct jffs2_sb_info *c, struct rb_root *list, uint32_t size);
 struct jffs2_raw_node_ref *jffs2_link_node_ref(struct jffs2_sb_info *c,
 					       struct jffs2_eraseblock *jeb,
 					       uint32_t ofs, uint32_t len,