[8chan] fix image urls

gallery_dl/extractor/8chan.py

@@ -4,7 +4,8 @@ import re
 
 class Extractor(BasicExtractor):
 
-    thread_url_fmt = "https://www.8ch.net/{0}/res/{1}.html"
+    url_base = "https://8ch.net"
+    thread_url_fmt = url_base + "/{0}/res/{1}.html"
     regex = r'>File: <a href="([^"]+)">([^<]+)\.[^<]+<.*?<span class="postfilename"( title="([^"]+)")?>([^<]+)<'
 
     def __init__(self, match, config):
@@ -18,4 +19,6 @@ class Extractor(BasicExtractor):
         text = self.request(url).text
         for match in re.finditer(self.regex, text):
             url, prefix, fullname, name = match.group(1, 2, 4, 5)
+            if url.startswith("/"):
+                url = self.url_base + url
             yield (url, prefix + "-" + unquote(fullname or name))