pulse-server: fix json comma handling

First was never set to false, so we kept skipping the commas.

Fixes 393f3e6d05

src/modules/module-protocol-pulse/message-handler.c

@@ -74,6 +74,7 @@ static int bluez_card_object_message_handler(struct pw_manager *m, struct pw_man
 			fprintf(r, "%s{\"name\":\"%d\",\"description\":\"%s\"}",
 					first ? "" : ",",
 					(int)codecs[i].id, desc ? desc : "Unknown");
+			first = false;
 		}
 		fputc(']', r);