[PATCH v2 resend] msxml3: Null check url in parseURL.

[Jefferson Carpenter]

Considered adding IVBSAXXMLReader_parseURL to test_saxreader() instead 
of adding the function test_vb_saxreader() but ran into two problems: 1) 
ISAXXMLReader sometimes cannot be queried for IVBSAXXMLReader and 2) the 
EXPECT_REF lines in contentHandler_putDocumentLocator would need to be 
incremented to account for the additional reference.