ReadOnly clean should run only on Windows

kcc/comic2ebook.py

@@ -569,6 +569,7 @@ def getWorkFolder(afile):
             os.rmdir(workdir)   # needed for copytree() fails if dst already exists
             fullPath = os.path.join(workdir, 'OEBPS', 'Images')
             copytree(afile, fullPath)
+            if sys.platform == 'win32':
                 sanitizeTreeReadOnly(fullPath)
             return workdir
         except OSError: