bug symfony#59130 [AssetMapper] minor fixes for pre-compression (dunglas)

This PR was merged into the 7.3 branch.

Discussion
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[AssetMapper] minor fixes for pre-compression

| Q             | A
| ------------- | ---
| Branch?       | 7.3
| Bug fix?      | yes
| New feature?  | no
| Deprecations? | no
| Issues        | symfony#59020 (review)
| License       | MIT

Fixes `@stof`'s comments.

Commits
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b6597b6 [AssetMapper] minor fixes for pre-compression

Author: fabpot

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
      */