Setting `show_small_image` to False breaks LazyImage for the whole page

[danielsamuels]

Disabling show_small_image results in the small image element not being output, as expected:

django-lazy-image/django_lazy_image/templates/django_lazy_image/lazy-image.html

Lines 6 to 8 in a4b1f78

	{% if show_small_image %}
	<img class="img-Image_Image img-Image_Image-small img-Image_Image-loaded{% if blur %} img-Image_Image-blurred{% endif %}" alt="" src="{{ small_image_url }}">
	{% endif %}

However, the JS will still try and remove this element, regardless of whether it exists or not:

django-lazy-image/assets/js/lazy-image.js

Lines 15 to 17 in a4b1f78

	if (evt.propertyName === 'opacity') {
	this.smallImage.parentNode.removeChild(this.smallImage)
	}

I think the above condition just needs to be changed to this:

if (evt.propertyName === 'opacity' && this.smallImage) {

[dan-gamble]

Had to recently do this on CSP. Will fix it now 👍

[dan-gamble]

This is live under 0.3.2 now. (Pypi and npm)