Fix extracting of several archives.

- Archive already existing must not stop download of other archives.
- Use copytree instead of rename to use second archive as patch on existing
  directory. (No need to remove tmpdir, as it is a temporary directory)

kiwixbuild/dependencies/base.py

@@ -131,8 +131,17 @@ class ReleaseDownload(Source):
 
     def _download(self, context):
         context.try_skip(neutralEnv("archive_dir"), self.full_name)
-        for archive in self.archives:
-            neutralEnv("download")(archive)
+        archive_iter = iter(self.archives)
+        archive = next(archive_iter, None)
+        while archive:
+            try:
+                neutralEnv("download")(archive)
+            except SkipCommand as e:
+                archive = next(archive_iter, None)
+                if not archive:
+                    raise e
+                continue
+            archive = next(archive_iter, None)
 
     def _extract(self, context):
         context.try_skip(self.extract_path)