fix cookie checks for patreon, fanbox, fantia

The changes in 9a255344 caused a warning about missing cookies to be
displayed even if those cookies were present, because _check_cookies()
did not account for an empty cookiedomain.

gallery_dl/extractor/common.py

@@ -336,7 +336,8 @@ class Extractor():
         now = time.time()
 
         for cookie in self._cookiejar:
-            if cookie.name in names and cookie.domain == domain:
+            if cookie.name in names and (
+                    not domain or cookie.domain == domain):
                 if cookie.expires and cookie.expires < now:
                     self.log.warning("Cookie '%s' has expired", cookie.name)
                 else: