gguf-py : Fix disconnect-before-connect crash on Kubuntu

[danielzgtg]

This fixes the crash upon load with venvs created with --system-site-packages to use python3-pyside6.qtwidgets=python3-pyside6.qtwidgets=6.6.2-4 from Kubuntu 24.10. Using system Qt is not merely æsthetic; I need Qt to use KDE's file picker so that hidden folders are openable. For users on other platforms, this doesn't change anything or just improves correctness.

Before

$ gguf-editor-gui
Traceback (most recent call last):
  File "/home/home/CLionProjects/llamacpprocm/gguf-py/gguf/scripts/gguf_editor_gui.py", line 913, in load_file
    self.load_metadata()
  File "/home/home/CLionProjects/llamacpprocm/gguf-py/gguf/scripts/gguf_editor_gui.py", line 948, in load_metadata
    self.metadata_table.itemChanged.disconnect(self.on_metadata_changed)
RuntimeError: Failed to disconnect (<bound method GGUFEditorWindow.on_metadata_changed of <gguf.scripts.gguf_editor_gui.GGUFEditorWindow(0x3fe2f560) at 0x7f5754e84480>>) from signal "itemChanged(QTableWidgetItem*)".

After

I was able to view gemma-3-4b-it-Q4_K_M.gguf successfully.