Fix index-out-of-bounds exception for splines

[HansOlsson]

When compiling with VS 2019 the following models crash: ModelicaTest.Tables.CombiTable2D[sv].Test2[167]

I believe it is an indexing issue - and have tried to correct the issue; it may be wrong - but there is clearly a major issue. The confusion is that we are sending in nRows-1 as nRows and then constructing nRows-1, i.e. nRows-2.

[beutlich]

Thanks for reporting. Need to investigate later.

[TManikantan]

@sjoelund would you please review the fix and approve it? It just requires one more review to merge it.