fix: Image::save() causes error with webp

imagewebp(): Palette image not supported by webp

Author: kenjis

system/Images/Handlers/GDHandler.php

@@ -227,6 +227,7 @@ public function save(?string $target = null, int $quality = 90): bool
 
         // for png and webp we can actually preserve transparency
         if (in_array($this->image()->imageType, $this->supportTransparency, true)) {
+            imagepalettetotruecolor($this->resource);
             imagealphablending($this->resource, false);
             imagesavealpha($this->resource, true);
         }

tests/_support/Images/rocket.png

@@ -412,6 +412,15 @@ public function testImageConvert(): void
         $this->assertSame(exif_imagetype($this->start . 'work/ci-logo.png'), IMAGETYPE_PNG);
     }
 
+    public function testImageConvertPngToWebp(): void
+    {
+        $this->handler->withFile($this->origin . 'rocket.png');
+        $this->handler->convert(IMAGETYPE_WEBP);
+        $saved = $this->start . 'work/rocket.webp';
+        $this->handler->save($saved);
+        $this->assertSame(exif_imagetype($saved), IMAGETYPE_WEBP);
+    }
+
     public function testImageReorientLandscape(): void
     {
         for ($i = 0; $i <= 8; $i++) {