Add exception when imageftbox() fails

Author: olivervogel

src/Drivers/Gd/FontProcessor.php

@@ -53,6 +53,10 @@ public function boxSize(string $text, FontInterface $font): SizeInterface
             string: $text,
         );
 
+        if ($box === false) {
+            throw new FontException('Unable to calculate box size of font ' . $font->filename() . '.');
+        }
+
         // build size from points
         return new Rectangle(
             width: intval(abs($box[6] - $box[4])), // difference of upper-left-x and upper-right-x