Fix issue with GD and relative font paths

This patch builds full path to a font file with GD driver to make sure
to pass absolute path to imageftbbox(). This is because of issues with
different GD versions behaving differently when passing relative paths
to imageftbbox()

Author: olivervogel

src/Drivers/Gd/FontProcessor.php

@@ -5,6 +5,7 @@
 namespace Intervention\Image\Drivers\Gd;
 
 use Intervention\Image\Drivers\AbstractFontProcessor;
+use Intervention\Image\Exceptions\FontException;
 use Intervention\Image\Geometry\Point;
 use Intervention\Image\Geometry\Rectangle;
 use Intervention\Image\Interfaces\FontInterface;
@@ -36,12 +37,20 @@ public function boxSize(string $text, FontInterface $font): SizeInterface
             return $box;
         }
 
+        // build full path to font file to make sure to pass absolute path to imageftbbox()
+        // because of issues with different GD version behaving differently when passing
+        // relative paths to imageftbbox()
+        $fontPath = realpath($font->filename());
+        if ($fontPath === false) {
+            throw new FontException('Font file ' . $font->filename() . ' does not exist.');
+        }
+
         // calculate box size from ttf font file with angle 0
         $box = imageftbbox(
             size: $this->nativeFontSize($font),
             angle: 0,
-            font_filename: $font->filename(),
-            string: $text
+            font_filename: $fontPath,
+            string: $text,
         );
 
         // build size from points