[mastodon] reset 'params' after first pagination iteration

otherwise query parameters in 'params' get specified twice the second
time around - once from the 'links["next"]' URL and once from 'params'
itself.

gallery_dl/extractor/mastodon.py

@@ -208,6 +208,7 @@ class MastodonAPI():
             if not url:
                 return
             url = url["url"]
+            params = None
 
 
 @cache(maxage=100*365*24*3600, keyarg=0)