fix: Initialise $result in write_log() to handle an empty log message. Fix #46.

system/core/Log.php

@@ -231,7 +231,7 @@ public function write_log($level, $msg)
 
 		$message .= $this->_format_line($level, $date, $msg);
 
-		for ($written = 0, $length = self::strlen($message); $written < $length; $written += $result)
+		for ($result = $written = 0, $length = self::strlen($message); $written < $length; $written += $result)
 		{
 			if (($result = fwrite($fp, self::substr($message, $written))) === FALSE)
 			{

tests/codeigniter/core/Log_test.php

@@ -92,4 +92,25 @@ public function test_format_line()
 			"LEVEL - Timestamp --> Message".PHP_EOL
 		);
 	}
+
+	public function test_write_log_with_empty_message()
+	{
+		$this->ci_set_config('log_path', '');
+		$this->ci_set_config('log_threshold', 4);
+		$this->ci_set_config('log_filename', 'empty.log');
+		$instance = new Log_empty_format_stub();
+
+		// _format_line() is overridden to return '', so $message is empty and the
+		// write loop never runs. Without $result initialised, is_int($result) returns FALSE,
+		// and write_log() wrongly returns FALSE.
+		$this->assertTrue($instance->write_log('error', 'discarded'));
+	}
+}
+
+class Log_empty_format_stub extends CI_Log {
+
+	protected function _format_line($level, $date, $message)
+	{
+		return '';
+	}
 }