Valgrind was reporting an uninitialized read for bad input.

This fixes the problem and the test passes.  I'm not sure
the test is really correct though.  It seems like it would
be better to raise an exception.  I think that wasn't done
for backwards compatability.

Bugfix candidate.

Modules/binascii.c

@@ -204,7 +204,8 @@ binascii_a2b_uu(PyObject *self, PyObject *args)
 	bin_data = (unsigned char *)PyString_AsString(rv);
 
 	for( ; bin_len > 0 ; ascii_len--, ascii_data++ ) {
-		this_ch = *ascii_data;
+		/* XXX is it really best to add NULs if there's no more data */
+		this_ch = (ascii_len > 0) ? *ascii_data : 0;
 		if ( this_ch == '\n' || this_ch == '\r' || ascii_len <= 0) {
 			/*
 			** Whitespace. Assume some spaces got eaten at