Index: wp-includes/class-wp-image-editor-gd.php
===================================================================
--- wp-includes/class-wp-image-editor-gd.php	(revision 26816)
+++ wp-includes/class-wp-image-editor-gd.php	(working copy)
@@ -205,7 +205,7 @@
 		$orig_size = $this->size;
 
 		foreach ( $sizes as $size => $size_data ) {
-			if ( ! ( isset( $size_data['width'] ) && isset( $size_data['height'] ) ) )
+			if ( ! isset( $size_data['width'] ) && ! isset( $size_data['height'] ) )
 				continue;
 
 			if ( ! isset( $size_data['crop'] ) )
Index: wp-includes/class-wp-image-editor-imagick.php
===================================================================
--- wp-includes/class-wp-image-editor-imagick.php	(revision 26816)
+++ wp-includes/class-wp-image-editor-imagick.php	(working copy)
@@ -272,7 +272,7 @@
 			if ( ! $this->image )
 				$this->image = $orig_image->getImage();
 
-			if ( ! ( isset( $size_data['width'] ) && isset( $size_data['height'] ) ) )
+			if ( ! isset( $size_data['width'] ) && ! isset( $size_data['height'] ) )
 				continue;
 
 			if ( ! isset( $size_data['crop'] ) )