follow-up r88171 - fix fatal if suggested filename has illegal character in it.

follow-up r88171 - fix fatal if suggested filename has illegal character in it.

Check to make sure the title object actual exists, before checking its namespace,
since alll the does this have illegal chars check is done after the does it
start with file: check.

For future note though, when using upload by url feature, the suggested
destination name when you put http://upload.wikimedia.org/wikipedia/commons/e/e0/Petrorhagia_prolifera_%281%29.JPG is illegal, which is probably not very user-friendly (filed as bug 30390)