Avoid background crash when fixing the tmux layout

scripts/wk/ui/tmux.py

@@ -129,7 +129,12 @@ def get_pane_size(pane_id: str | None = None) -> tuple[int, int]:
 
   # Get resolution
   proc = run_program(cmd, check=False)
+  try:
     width, height = proc.stdout.strip().split()
+  except ValueError:
+    # Assuming this is a race condition as it usually happens inside the
+    # background fix layout loop
+    return 0, 0
   width = int(width)
   height = int(height)