Fix MAGN-3732 Curve doesn't update if it was selected using SelectModeEl...

@lukechurch 

This submission incorporates the fix in https://github.com/DynamoDS/Dynamo/pull/2090, the comments and the fix in https://github.com/DynamoDS/Dynamo/commit/6a5a989db5460fddbf9d02322d8127490173c911#diff-fbcecd4dfc35ed3c3ade173b1006e4ceR62 to fix MAGN-3732.

@lukechurch 

This is added to address the performance issue.