When parsing results from a .csv file skip over any results that are invalid

#### Description:

Results cannot be read when invalid or empty results are present:

#### Steps to reproduce:

1. Push model with loads and `Loadcases` that can be solved
2. Create empty `Loadcase` with no loads applied
3. Attempt to pPull `NodeReaction`

#### Expected behaviour:

Allow user to pull `NodeReaction` despite empty `Loadcase`

#### Test file(s):

Start by tracing how CSV results for NodeReaction are parsed and how empty Loadcases are represented. Use the listed reproduction steps with a model containing solvable and empty Loadcases, then verify that invalid or empty results are skipped while valid results remain available to pull.

Written by the indexing model from the issue text.