fix(handler): handle false positives YAFFS sample by checking entries.

We have a YAFFS false positive sample that gets parsed but triggers a
NodeIDAbsentError when calling
'self.file_entries.expand_tree(mode=Tree.DEPTH)' during extraction. This
exception is raised by treelib if the tree is empty.

We handle this edge case by checking if the tree is empty after the
chunk identification, and raise an InvalidInputFormat if it is.

Author: qkaiser

unblob/handlers/filesystem/yaffs.py

@@ -299,6 +299,7 @@ def init_tree(self):
 
     def parse(self, store: bool = False):  # noqa: C901,FBT001,FBT002
         self.init_tree()
+        entries = 0
         for offset, page, spare in iterate_over_file(self.file, self.config):
             try:
                 data_chunk = self.build_chunk(
@@ -325,8 +326,11 @@ def parse(self, store: bool = False):  # noqa: C901,FBT001,FBT002
 
                 if store:
                     self.insert_entry(self.build_entry(header, data_chunk))
+                entries += 1
             elif store:
                 self.data_chunks[data_chunk.object_id].append(data_chunk)
+        if not entries:
+            raise InvalidInputFormat("YAFFS filesystem with no entries.")
         self.end_offset = self.file.tell()
 
     def auto_detect(self) -> YAFFSConfig: