Fix null deref in legacy SAX1 parser
Always call nameNsPush instead of namePush. The latter is unused now and should probably be removed from the public API. I can't see how it could be used reasonably from client code and the unprefixed name has always polluted the global namespace. Fixes a null pointer dereference introduced with de5b624f when parsing in SAX1 mode. Found by OSS-Fuzz.