Don't show thumbnail video symbol for HEIC photos

[watsonbox]

Since Piwigo 14's HEIC support, HEIC thumbnails show a video symbol:

That seems to be because they have pwg_representitive files which, like videos, they require to be rendered in all browsers.

piwigo-bootstrap-darkroom/template/index.tpl

Lines 310 to 312 in 012aeb6

	$('.card-thumbnail').find('img[src*="pwg_representative"]').each(function() {
	$(this).closest('div').append('<i class="fas fa-file-video fa-2x video-indicator" aria-hidden="true" style="position: absolute; top: 10px; left: 10px; z-index: 100; color: #fff;"></i>');
	});

This PR excludes thumbnail cards with a file-ext-heic class: