fixes #58 UnpooledDataSource does not use custom driver properties when acquiring connection. I couldn't find a way to write a test for this.

Author: harawata

src/main/java/org/apache/ibatis/datasource/unpooled/UnpooledDataSource.java

@@ -173,7 +173,10 @@ public void setDefaultTransactionIsolationLevel(Integer defaultTransactionIsolat
   }
 
   private Connection doGetConnection(String username, String password) throws SQLException {
-    Properties props = new Properties(driverProperties);
+    Properties props = new Properties();
+    if (driverProperties != null) {
+      props.putAll(driverProperties);
+    }
     if (username != null) {
       props.setProperty("user", username);
     }