nginx: Do not attempt to parse and rewrite our URLs, please

deployment/docker/nginx.conf

@@ -68,7 +68,14 @@ http {
             add_header Cache-Control "public";
         }
         location / {
-            proxy_pass http://unix:/tmp/pretix.sock:/;
+            # Very important:
+            #   proxy_pass http://unix:/tmp/pretix.sock:;
+            # is not the same as
+            #   proxy_pass http://unix:/tmp/pretix.sock:/;
+            # In the latter case, nginx will apply its URL parsing, in the former it doesn't.
+            # There are situations in which pretix' API will deal with "file names" containing %2F%2F, which
+            # nginx will normalize to %2F, which can break ticket validation.
+            proxy_pass http://unix:/tmp/pretix.sock:;
             proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
         	proxy_set_header Host $http_host;
         }