DeriveParameters caches missing stored procedures

[nhathongly]

These are my steps to reproduce the issue:

1. In my running web app, call MySqlCommandBuilder.DeriveParametersAsync to get parameters of an **nonexistent ** stored procedure, then I get a MySqlException which its message is ""Procedure or function 'ABC' cannot be found in database 'XYZ'."
2. I deploy the stored procedure 'ABC' to the database 'XYZ' while the web app is running
3. Call MySqlCommandBuilder.DeriveParametersAsync to get parameters of stored procedure 'ABC' again and still get the exception
4. Restart my web app, and the exception is gone

It seems the cachedProcedure should be checked if it's null before storing it in cachedProcedures

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

Lines 533 to 537 in 2d5189a

	lock (cachedProcedures)
	{
	cachedProcedures[normalized.FullyQualified] = cachedProcedure;
	count = cachedProcedures.Count;
	}

[bgrainger]

null needs to be stored in cachedProcedures as an optimisation for DB server versions that don't support retrieving parameter metadata. (Otherwise, overhead is incurred on every stored procedure execution.)

But it seems that DeriveParameters could always revalidate the stored procedure since this is an explicit action by the user.

[bgrainger]

Fixed in 0.60.3.