When reading a region, use null objects to represent NULL fields.

Previously NULL fields were converted to an empty string due to the use of ToString(). But if the field was an Int (e.g., "locZ"), then the subsequent attempt to convert an empty string to an int caused an exception. Now the field is null so we don't try to convert it, so there's no exception.

OpenSim/Data/MySQL/MySQLRegionData.cs

@@ -187,6 +187,10 @@ namespace OpenSim.Data.MySQL
                             if (s == "locY")
                                 continue;
 
+                            object value = result[s];
+                            if (value is DBNull)
+                                ret.Data[s] = null;
+                            else
                                 ret.Data[s] = result[s].ToString();
                         }