warc: Fix CDX fields missing with multi-line HTTP headers

The regex used to find the end of the HTTP headers would not match if
there was a newline in between, so get_http_header would return nothing
and the status code and MIME type fields would be empty in the CDX record.

wpull/warc/format.py

@@ -163,7 +163,7 @@ def get_http_header(self) -> Response:
         with wpull.util.reset_file_offset(self.block_file):
             data = self.block_file.read(4096)
 
-        match = re.match(br'(.*?\r?\n\r?\n)', data)
+        match = re.match(br'(.*?\r?\n\r?\n)', data, re.DOTALL)
 
         if not match:
             return