Don't print whole json data buffer to errorstream on error

`errorstream` must not be overly verbose as clientside it is directly printed
onto the ingame chat window. These days, the serverlist can contain > 200k bytes,
so better print it to warningstream if the data buffer is too long.

src/convert_json.cpp

@@ -52,7 +52,13 @@ Json::Value fetchJsonValue(const std::string &url,
 	if (!reader.parse(stream, root)) {
 		errorstream << "URL: " << url << std::endl;
 		errorstream << "Failed to parse json data " << reader.getFormattedErrorMessages();
-		errorstream << "data: \"" << fetch_result.data << "\"" << std::endl;
+		if (fetch_result.data.size() > 100) {
+			errorstream << "Data (" << fetch_result.data.size()
+				<< " bytes) printed to warningstream." << std::endl;
+			warningstream << "data: \"" << fetch_result.data << "\"" << std::endl;
+		} else {
+			errorstream << "data: \"" << fetch_result.data << "\"" << std::endl;
+		}
 		return Json::Value();
 	}
 

src/script/lua_api/l_util.cpp

@@ -161,8 +161,14 @@ int ModApiUtil::l_parse_json(lua_State *L)
 		if (!reader.parse(stream, root)) {
 			errorstream << "Failed to parse json data "
 				<< reader.getFormattedErrorMessages();
-			errorstream << "data: \"" << jsonstr << "\""
-				<< std::endl;
+			size_t jlen = strlen(jsonstr);
+			if (jlen > 100) {
+				errorstream << "Data (" << jlen
+					<< " bytes) printed to warningstream." << std::endl;
+				warningstream << "data: \"" << jsonstr << "\"" << std::endl;
+			} else {
+				errorstream << "data: \"" << jsonstr << "\"" << std::endl;
+			}
 			lua_pushnil(L);
 			return 1;
 		}