Improve leniency in Number parsing (enclosure length)

Description

Number parsing in ROME is currently fairly brittle in many places. While it's
frequently acceptable for numeric properties to be absent, if they are
unparsable a NUmberFormatException is thrown.

It seems like it would be more prudent to treat the situations equivilently.

A specific example seen in the wild (http://feeds.wired.com/GearFactor) is
RSS feeds where some <enclosure> tags have length attributes of "unknown".

patch to follow

Environment

None

Status

Assignee

ROME Jira Lead

Reporter

hossman

Labels

None

Participants

None

Fix versions

Affects versions

current

Priority

Major