REDHAT-BUG-2443262: High severity JBoss Undertow vulnerability

When Undertow receives a request in which the first header line begins with one or more spaces, it strips them before processing the request. This is usable as a request smuggling primitive.

The HTTP RFCs state that when a field-line begins with a space or tab, it is permissible to concatenate it into the previous field-line's value. This is referred to as obs-fold in the RFCs. However, it is always invalid to obs-fold on the first line, since there is no previous field-line to concatenate into. Thus, the message should be rejected.