Answer an oversized RPC response with a fault

Cap XML-RPC and JSON-RPC output at the SCGI response limit before handing it over.

src/rpc/scgi_task.h

@@ -2,6 +2,7 @@
 #define RTORRENT_RPC_SCGI_TASK_H
 
 #include <chrono>
+#include <cstdint>
 #include <memory>
 #include <mutex>
 #include <vector>
@@ -18,6 +19,8 @@ public:
   static constexpr int max_header_size     = 2000;
   static constexpr int max_content_size    = (1 << 26);
 
+  static constexpr uint32_t max_response_size = (100 << 20);
+
   static constexpr auto timeout_request = std::chrono::seconds(60);
 
   enum ContentType { XML, JSON };