Robot_Toolkit: More than selected cases run for AnalyseLoadcses

#### Description:

As description says, found by @kThorsager here https://github.com/BHoM/Robot_Toolkit/pull/293#pullrequestreview-347853243

#### How to replicate:

Push multiple loadcases and use the AnalyseLoadcases to try so run only one of them. For some cases, more than the selected case will be run.

#### Expected behaviour:

For only selected cases to be run

#### Test file(s):

Start with the AnalyseLoadcases entry point and the reproduction described in PR #293's review. Trace how selected loadcases are handled when multiple loadcases are pushed. Done means running AnalyseLoadcases with multiple loadcases executes only the selected case; the issue does not identify a test file.

Written by the indexing model from the issue text.