Slightly optimize show_toolbar()
Slightly optimize show_toolbar()

Avoid inspecting the request if `DEBUG` is not `True`, and remove unnecessary cast to `bool`.

jazzband/django-debug-toolbar,tim-schilling/django-debug-toolbar,jazzband/django-debug-toolbar,django-debug-toolbar/django-debug-toolbar,tim-schilling/django-debug-toolbar,spookylukey/django-debug-toolbar,tim-schilling/django-debug-toolbar,spookylukey/django-debug-toolbar,spookylukey/django-debug-toolbar,jazzband/django-debug-toolbar,django-debug-toolbar/django-debug-toolbar,django-debug-toolbar/django-debug-toolbar