Make sure value implements IConvertible before attempting to use Convert.ChangeType() (#35)

When returning values, conversion was attempted using the IConvertible interface, but without first checking if the value implemented IConvertible - leading to an exception in the case(s) where IConvertible was not implemented.

This change adds a test around the conversion attempt, to ensure conversion by IConvertible is only attempted on values that implement IConvertible.

Author: gtbX

NuoDb.Data.Client/NuoDbDataReader.cs

@@ -586,7 +586,11 @@ public virtual T GetFieldValue<T>(int ordinal)
             {
                 return default(T);
             }
-            return (T)Convert.ChangeType(getValue(ordinal).Object, typeof(T));
+            if (value is IConvertible)
+            {
+                return (T)Convert.ChangeType(value, typeof(T));
+            }
+            return (T)value;
         }
 
         public virtual T GetFieldValue<T>(string name)
@@ -629,7 +633,7 @@ public override object GetValue(int i)
                 {
                     return GetGuid(i);
                 }
-                else
+                else if (value is IConvertible)
                 {
                     return Convert.ChangeType(value, declaredType);
                 }