Why not to pre-select category on the bug_report page if only the one category exists?

print_api.php
print_category_option_list()

Now:

foreach( $cat_arr as $t_category_row ) {

...

Tweak:

$cnt = count($cat_arr);

if ($cnt == 1)

$p_category_id = $cat_arr[0]['id'];

foreach( $cat_arr as $t_category_row ) {

...