Fix random order page change issue.

I bet you thought all of the random order gateway test issues were
resolved.  Nope.

When a page change occurs in a random order test, the answers saved in
the hidden inputs for the problems not on the current page are still not
respecting the order.  As a result the answers get moved around to
incorrect problems each time that a page change occurs.

Author: drgrice1

lib/WeBWorK/ContentGenerator/GatewayQuiz.pm

@@ -971,7 +971,7 @@ async sub pre_header_initialize ($c) {
 					create_ans_str_from_responses($c->{formFields}, $pg_result,
 						$pureProblem->flags =~ /:needs_grading/);
 			} else {
-				my $prefix         = sprintf('Q%04d_', $problemNumbers[$i]);
+				my $prefix         = sprintf('Q%04d_', $problemNumbers[ $probOrder[$i] ]);
 				my @fields         = sort grep {/^(?!previous).*$prefix/} (keys %{ $c->{formFields} });
 				my %answersToStore = map       { $_ => $c->{formFields}->{$_} } @fields;
 				my @answer_order   = @fields;