Tolerate package html directories being owned by someone else

As a consequence of the cygwin-admin/cygwin split, we might not own an
existing package listing/summary HTML directory. Ignore any error trying
to set permissions in that case.

calm/pkg2html.py

@@ -125,7 +125,10 @@ def arch_packages(packages, p):
 def ensure_dir_exists(args, path):
     if not args.dryrun:
         utils.makedirs(path)
-        os.chmod(path, 0o755)
+        try:
+            os.chmod(path, 0o755)
+        except PermissionError:
+            pass
 
 
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