Throw from Prepare if CommandText isn't set.

Author: bgrainger

src/MySqlConnector/MySql.Data.MySqlClient/MySqlCommand.cs

@@ -76,6 +76,8 @@ public override void Prepare()
 				throw new InvalidOperationException("Connection property must be non-null.");
 			if (Connection.State != ConnectionState.Open)
 				throw new InvalidOperationException("Connection must be Open; current state is {0}".FormatInvariant(Connection.State));
+			if (string.IsNullOrWhiteSpace(CommandText))
+				throw new InvalidOperationException("CommandText must be specified");
 
 			// NOTE: Prepared statements in MySQL are not currently supported.
 			// 1) Only a subset of statements are actually preparable by the server: http://dev.mysql.com/worklog/task/?id=2871