"Bug Detected" warning appears when running mypaint

[krishauga]

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Description of the problem

"Bug Detected" warning appears as indicated below when running mypaint

Basic system details

MyPaint version: Mypaint version: 2.0.1+gitexport.478280f
Operating system: Linux-6.1.0-rpi6-rpi-v8-aarch64-with-glibc2.36
Using: Python 3.11.2, GTK 3.24.38, GdkPixbuf 2.42.10, Cairo 1.16.0, GLib 2.74.4

Steps to reproduce

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1. Start MyPaint - "Bug Detected" warning appears as indicated below

Backtraces or error messages

```python
Mypaint version: 2.0.1+gitexport.478280f
System information: Linux-6.1.0-rpi6-rpi-v8-aarch64-with-glibc2.36
Using: Python 3.11.2, GTK 3.24.38, GdkPixbuf 2.42.10, Cairo 1.16.0, GLib 2.74.4
Traceback (most recent call last):
  File "/usr/lib/mypaint/gui/application.py", line 488, _at_application_start(self=<gui.application.Application object>, filenames=[], fullscreen=None)
                autosave_recovery = gui.autorecover.Presenter(self)
                autosave_recovery.run(startup=True)
  variables: {'autosave_recovery.run': ('local', <bound method Presenter.run of <gui.autorecover.Presenter object at 0x7f98ac2a10>>), 'startup': (None, [])}
  File "/usr/lib/mypaint/gui/autorecover.py", line 133, run(self=<gui.autorecover.Presenter object>, startup=True)
            # Only run if there are autosaves which can be recovered.
            autosaves = self._reload_liststore()
            if not autosaves:
  variables: {'autosaves': (None, []), 'self._reload_liststore': ('local', <bound method Presenter._reload_liststore of <gui.autorecover.Presenter object at 0x7f98ac2a10>>)}
  File "/usr/lib/mypaint/gui/autorecover.py", line 79, _reload_liststore(self=<gui.autorecover.Presenter object>)
            autosaves = []
            for asav in lib.document.get_available_autosaves():
                # Another instance may be working in there.
  variables: {'asav': (None, []), 'lib.document.get_available_autosaves': ('global', <function get_available_autosaves at 0x7f945a9300>)}
  File "/usr/lib/mypaint/lib/document.py", line 2196, get_available_autosaves()
                continue
            yield AutosaveInfo.new_for_path(autosave_path)
  variables: {'AutosaveInfo.new_for_path': ('global', <bound method AutosaveInfo.new_for_path of <class 'lib.document.AutosaveInfo'>>), 'autosave_path': ('local', '/home/annapi/.cache/mypaint/doc.af9sf0r7/autosave')}
  File "/usr/lib/mypaint/lib/document.py", line 170, new_for_path(cls=<class 'lib.document.AutosaveInfo'>, path='/home/annapi/.cache/mypaint/doc.af9sf0r7/autosave')
            if os.path.exists(thumbnail_path):
                thumbnail = lib.pixbuf.load_from_file(thumbnail_path)
            cache_in_use = False
  variables: {'thumbnail': ('local', None), 'lib.pixbuf.load_from_file': ('global', <function load_from_file at 0x7f98aecae0>), 'thumbnail_path': ('local', '/home/annapi/.cache/mypaint/doc.af9sf0r7/autosave/Thumbnails/thumbnail.png')}
  File "/usr/lib/mypaint/lib/pixbuf.py", line 114, load_from_file(filename='/home/annapi/.cache/mypaint/doc.af9sf0r7/autosave/Thumbnails/thumbnail.png', progress=<Progress 0.0/0>)
            progress.items = size
            pixbuf = load_from_stream(fp, progress=progress)
  variables: {'pixbuf': (None, []), 'load_from_stream': ('global', <function load_from_stream at 0x7f947be700>), 'fp': ('local', <_io.BufferedReader name='/home/annapi/.cache/mypaint/doc.af9sf0r7/autosave/Thumbnails/thumbnail.png'>), 'progress': ('local', <Progress 0.0/0>)}
  File "/usr/lib/mypaint/lib/pixbuf.py", line 150, load_from_stream(fp=<_io.BufferedReader name='/home/annapi/.cache/my.../doc.af9sf0r7/autosave/Thumbnails/thumbnail.png'>, progress=<Progress 0.0/0>)
                progress += len(buf)
        loader.close()
        return loader.get_pixbuf()
  variables: {'loader.close': ('local', gi.FunctionInfo(close))}
Error: gdk-pixbuf-error-quark: Unrecognized image file format (3)