Fix YAML duplicate keys, add credit and parsing tip

CHANGELOG.md

@@ -6,6 +6,11 @@ This change log follows the conventions of
 
 ## [Unreleased][unreleased]
 
+### Added
+
+- Thanks to [Dominik Stolz (@voidc)](https://github.com/voidc), we can now
+  parse `exportExt.pdb` files for the tag information they contain.
+
 ### Fixed
 
 - An error in interpreting a value in the database export file format could lead to some rows that were actually present in tables not being found. Thanks to [@IvanOnishchenko](https://github.com/IvanOnishchenko) for [pointing this out](https://github.com/Deep-Symmetry/crate-digger/issues/32), and [Jan Holthuis (@Holzhaus)](https://github.com/Holzhaus) for identifying a flaw in the first attempt at correcting it.

README.adoc

@@ -109,6 +109,20 @@ line of the listing, then tell your browser to save it to disk. Be
 sure to keep the `.ksy` extension. Then you can upload it to the
 Kaitai Struct Web IDE.
 
+If you want to look at an `exportExt.pdb` file, follow the procedure above but then also put the following content into an auxiliary file (named
+something like `redkordboxExt_pdb.ksy`) and drag it into the web IDE before
+you drag in the database, that will tell the web IDE which variant of the
+file it is working with:
+
+```yaml
+meta:
+  id: rekordbox_pdb_ext
+  imports:
+    - rekordbox_pdb
+seq:
+  - id: root
+    type: rekordbox_pdb(true)
+```
 
 == ANLZ Data
 

src/main/kaitai/rekordbox_pdb.ksy

@@ -344,7 +344,7 @@ types:
         -webide-parse-mode: eager
       body:
         pos: row_base
-        if: not _root.is_ext
+        if: present and not _root.is_ext
         type:
           switch-on: _parent._parent.type
           cases:
@@ -360,19 +360,17 @@ types:
             'page_type::history_playlists': history_playlist_row
             'page_type::history_entries': history_entry_row
             'page_type::tracks': track_row
-        if: present
         doc: |
           The actual content of the row, as long as it is present.
         -webide-parse-mode: eager
       body_ext:
         pos: row_base
-        if: _root.is_ext
+        if: present and _root.is_ext
         type:
           switch-on: _parent._parent.type_ext
           cases:
             'page_type_ext::tags': tag_row
             'page_type_ext::tag_tracks': tag_track_row
-        if: present
         doc: |
           The actual content of the row, as long as it is present.
         -webide-parse-mode: eager