Merge 1.42 from PyXML: Flag errors resulting from argument conversion problems.
Fixes problem with not detecting UTF-8 errors.
diff --git a/Modules/pyexpat.c b/Modules/pyexpat.c
index db4333c..96cb79d 100644
--- a/Modules/pyexpat.c
+++ b/Modules/pyexpat.c
@@ -475,8 +475,7 @@
     if (self->handlers[NAME] \
         && self->handlers[NAME] != Py_None) { \
         args = Py_BuildValue PARAM_FORMAT ;\
-        if (!args) \
-            return RETURN; \
+        if (!args) { flag_error(self); return RETURN;} \
         self->in_callback = 1; \
         rv = call_with_frame(getcode(NAME,#NAME,__LINE__), \
                              self->handlers[NAME], args); \