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 imagettftext(). This is because of issues with
different GD versions behaving differently when passing relative paths
to imagettftext()

Author: olivervogel

src/Drivers/Gd/Modifiers/TextModifier.php

@@ -5,6 +5,7 @@
 namespace Intervention\Image\Drivers\Gd\Modifiers;
 
 use Intervention\Image\Exceptions\ColorException;
+use Intervention\Image\Exceptions\FontException;
 use Intervention\Image\Exceptions\RuntimeException;
 use Intervention\Image\Interfaces\ImageInterface;
 use Intervention\Image\Interfaces\SpecializedInterface;
@@ -26,32 +27,40 @@ public function apply(ImageInterface $image): ImageInterface
         $textColor = $this->gdTextColor($image);
         $strokeColor = $this->gdStrokeColor($image);
 
+        // 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 imagettftext()
+        $fontPath = $this->font->hasFilename() ? realpath($this->font->filename()) : false;
+        if ($this->font->hasFilename() && $fontPath === false) {
+            throw new FontException('Font file ' . $this->font->filename() . ' does not exist.');
+        }
+
         foreach ($image as $frame) {
             imagealphablending($frame->native(), true);
             if ($this->font->hasFilename()) {
                 foreach ($lines as $line) {
                     foreach ($this->strokeOffsets($this->font) as $offset) {
                         imagettftext(
-                            $frame->native(),
-                            $fontProcessor->nativeFontSize($this->font),
-                            $this->font->angle() * -1,
-                            $line->position()->x() + $offset->x(),
-                            $line->position()->y() + $offset->y(),
-                            $strokeColor,
-                            $this->font->filename(),
-                            (string) $line
+                            image: $frame->native(),
+                            size: $fontProcessor->nativeFontSize($this->font),
+                            angle: $this->font->angle() * -1,
+                            x: $line->position()->x() + $offset->x(),
+                            y: $line->position()->y() + $offset->y(),
+                            color: $strokeColor,
+                            font_filename: $fontPath,
+                            text: (string) $line
                         );
                     }
 
                     imagettftext(
-                        $frame->native(),
-                        $fontProcessor->nativeFontSize($this->font),
-                        $this->font->angle() * -1,
-                        $line->position()->x(),
-                        $line->position()->y(),
-                        $textColor,
-                        $this->font->filename(),
-                        (string) $line
+                        image: $frame->native(),
+                        size: $fontProcessor->nativeFontSize($this->font),
+                        angle: $this->font->angle() * -1,
+                        x: $line->position()->x(),
+                        y: $line->position()->y(),
+                        color: $textColor,
+                        font_filename: $fontPath,
+                        text: (string) $line
                     );
                 }
             } else {