[IMPR] Simplify expression for old_position in Link.parse()
[IMPR] Simplify expression for old_position in Link.parse()

str.find(':') is not 0 if it not starts with that token. In that case
old_position should become 0 and 1 if it starts with ':'. This can be
simplified with int(str.startswith(':')) because int(True) is 1.

Change-Id: I97c474391c427287b2aaa68ee8ee392238e770d1

wikimedia/pywikibot-core,PersianWikipedia/pywikibot-core,wikimedia/pywikibot-core