[AssetMapper] minor fixes for pre-compression

Author: dunglas

src/Symfony/Component/AssetMapper/Compressor/GzipCompressor.php

@@ -22,7 +22,8 @@
 final class GzipCompressor implements SupportedCompressorInterface
 {
     use CompressorTrait {
-        compress as baseCompress;
+        compress as private baseCompress;
+        getUnsupportedReason as private baseGetUnsupportedReason;
     }
 
     private const WRAPPER = 'compress.zlib';
@@ -51,6 +52,15 @@ public function compress(string $path): void
         $this->baseCompress($path);
     }
 
+    public function getUnsupportedReason(): ?string
+    {
+        if (null === $this->zopfliCompressor->getUnsupportedReason()) {
+            return null;
+        }
+
+        return $this->baseGetUnsupportedReason();
+    }
+
     /**
      * @return resource
      */