Avoid doubly-compressing zstandard files

tests/test_blendfile_loading.py

@@ -283,7 +283,7 @@ class CompressionRecognitionTest(AbstractBlendFileTest):
     def _find_compression_type(self, filename: str) -> magic_compression.Compression:
         path = self.blendfiles / filename
         with path.open("rb") as fileobj:
-            return magic_compression._find_compression_type(fileobj)
+            return magic_compression.find_compression_type(fileobj)
 
     def test_gzip_recognition(self):
         comp = self._find_compression_type("basic_file_compressed.blend")

tests/test_compressor.py

@@ -68,6 +68,9 @@ class CompressorTest(AbstractBlendFileTest):
     def test_copy_already_compressed(self):
         self._test("basic_file_ñønæščii.blend", True)
 
+    def test_copy_zstandard_compressed(self):
+        self._test("basic_file_zstandard.blend", True)
+
     def test_copy_compress_on_the_fly(self):
         self._test("basic_file.blend", True)