Well,
I wrote a solution so writing it here:
/*
This action copies old theme's theme location saves to
new theme if new theme doesnt have saves before.
*/
add_action( 'after_switch_theme', 'ajx_theme_locations_rescue' );
function ajx_theme_locations_rescue() {
// bug report / support: http://www.unsalkorkmaz.com/
// We got old theme's slug name
$old_theme = get_option( 'theme_switched' );
// Getting old theme's settings
$old_theme_mods = get_option("theme_mods_{$old_theme}");
// Getting old theme's theme location settings
$old_theme_navs = $old_theme_mods['nav_menu_locations'];
// Getting new theme's theme location settings
$new_theme_navs = get_theme_mod( 'nav_menu_locations' );
// If new theme's theme location is empty (its not empty if theme was activated and set some theme locations before)
if (!$new_theme_navs) {
// Getting registered theme locations on new theme
$new_theme_locations = get_registered_nav_menus();
foreach ($new_theme_locations as $location => $description ) {
// We setting same nav menus for each theme location
$new_theme_navs[$location] = $old_theme_navs[$location];
}
set_theme_mod( 'nav_menu_locations', $new_theme_navs );
}
}