Fix bug that produces invalid XML plist
Fix bug that produces invalid XML plist

If a CFNumber(0) is serialized as XML, it produces an invalid XML node (<integer/>) which triggers a parse error in Apple's code. This code fixes this issue.
Tonyliu2ca/CFPropertyList,rodneyrehm/CFPropertyList,Tonyliu2ca/CFPropertyList,rodneyrehm/CFPropertyList