Bugfix/return client errors

[sashawood]

Handle 2 cases where bad client data cause a 500 Internal Server Error, rather than the nicer soap11env:Client.XMLSyntaxError.

Case 1: Client does not send body in its request. This causes an empty generator to be passed to _parse_xml_string, which causes an unhandled StopIteration exception.

Case 2: Client sends badly encoded data in its request. This causes a badly encoded byte string to be passed to _parse_xml_string, which causes a UnicodeDecodeError when we try to decode it.

[arskom-jenkins]

Can one of the admins verify this patch?

[plq]

hey, thanks for the patch. i'm sorry these seem to have totally evaded my attention, looking into these right now