storage: move check for enable_partial_images to GetDiffer

move the check for `enable_partial_images` to GetDiffer so that it
doesn't attempt any operation if the feature is disabled.

Signed-off-by: Giuseppe Scrivano <gscrivan@redhat.com>

pkg/chunked/storage_linux.go

@@ -241,6 +241,10 @@ func GetDiffer(ctx context.Context, store storage.Store, blobDigest digest.Diges
 		return nil, err
 	}
 
+	if !parseBooleanPullOption(&storeOpts, "enable_partial_images", true) {
+		return nil, errors.New("enable_partial_images not configured")
+	}
+
 	_, hasZstdChunkedTOC := annotations[internal.ManifestChecksumKey]
 	_, hasEstargzTOC := annotations[estargz.TOCJSONDigestAnnotation]
 
@@ -1701,10 +1705,6 @@ func (c *chunkedDiffer) ApplyDiff(dest string, options *archive.TarOptions, diff
 		UncompressedDigest: uncompressedDigest,
 	}
 
-	if !parseBooleanPullOption(c.storeOpts, "enable_partial_images", true) {
-		return output, errors.New("enable_partial_images not configured")
-	}
-
 	// When the hard links deduplication is used, file attributes are ignored because setting them
 	// modifies the source file as well.
 	useHardLinks := parseBooleanPullOption(c.storeOpts, "use_hard_links", false)