Media: Prevent unnecessary whitespace around PDF Thumbnails.

Stops unintended whitespace from showing around PDF thumbnails
when the PDF creation tool utilized a CropBox.

Props michelweimerskirch, joemcgill.
Fixes #45598.

git-svn-id: https://develop.svn.wordpress.org/trunk@46238 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/class-wp-image-editor-imagick.php

@@ -787,6 +787,10 @@ protected function pdf_setup() {
 			// We want the thumbnail to be readable, so increase the rendering DPI.
 			$this->image->setResolution( 128, 128 );
 
+			// When generating thumbnails from cropped PDF pages, Imagemagick uses the uncropped
+			// area (resulting in unnecessary whitespace) unless the following option is set.
+			$this->image->setOption( 'pdf:use-cropbox', true );
+
 			// Only load the first page.
 			return $this->file . '[0]';
 		} catch ( Exception $e ) {