Change to Boolean logic (#999)

modules/islandora_iiif/src/Plugin/views/style/IIIFManifest.php

@@ -343,7 +343,7 @@ class IIIFManifest extends StylePluginBase {
 
         // If this is a TIFF AND we don't know the width/height
         // see if we can get the image size via PHP's core function.
-        if ($mime_type === 'image/tiff' && !$width || !$height) {
+        if ($mime_type === 'image/tiff' && (!$width || !$height)) {
           $uri = $image->entity->getFileUri();
           $path = $this->fileSystem->realpath($uri);
           $image_size = getimagesize($path);