Preserve MySQL connection failures across queries

site/tests/services.uce

@@ -115,6 +115,15 @@ RENDER(Request& context)
 		parsed_underscore.find("'Ada'") != String::npos && parsed_underscore.find("_name") == String::npos ? "pass" : "fail",
 		parsed_underscore
 	);
+	MySQL unavailable_mysql;
+	unavailable_mysql.connect("127.0.0.1", "__uce_intentionally_missing__", "not-a-real-password");
+	unavailable_mysql.query("SELECT 1");
+	String unavailable_mysql_error = unavailable_mysql.error();
+	mark(
+		"mysql query after failed connect retains the connection error",
+		unavailable_mysql_error != "" ? "pass" : "fail",
+		unavailable_mysql_error
+	);
 
 	MySQL mysql;
 	mysql.connect("127.0.0.1", "root", "");

src/lib/mysql-connector.cpp

@@ -226,8 +226,10 @@ DValue MySQL::query(String q)
 	}
 	if(!connection)
 	{
-		_preload_next_error_code = CR_UNKNOWN_ERROR;
+		if(_preload_next_error_code == 0)
-		statement_info = "mysql connection is not open";
+			_preload_next_error_code = CR_UNKNOWN_ERROR;
+		if(statement_info == "")
+			statement_info = "mysql connection is not open";
 		return(DValue());
 	}
 	_preload_next_error_code = mysql_query((MYSQL*)connection, q.c_str());

src/wasm/core.cpp

@@ -287,6 +287,14 @@ DValue MySQL::query(String q)
 		statement_info = "mysql positional ? placeholders are not supported; use named :name placeholders";
 		return(DValue());
 	}
+	if(!connection)
+	{
+		if(_preload_next_error_code == 0)
+			_preload_next_error_code = 2000;
+		if(statement_info == "")
+			statement_info = "mysql connection is not open";
+		return(DValue());
+	}
 	DValue request;
 	request["op"] = "query";
 	request["handle"] = (f64)(uintptr_t)connection;