Added small utility to verify vector access

[kzscisoft]

Throws an exception if the container is size zero, prevents seg fault. This covers the case of the model being run without the data being available.

[peter-t-fox]

Unless I've missed something, it looks like this PR just duplicates functionality that it already present in the code?

[peter-t-fox]

I'm a little confused by this. It seems that checkAndGetSize is just doing a subset of what the ImportConsistencyCheck function is doing a few lines down? (The former only checks that there are a non-zero number of rows in observations.cases; the latter checks that there are exactly the correct number of rows and columns).

[kzscisoft]

The current ordering will cause a memory issue if the number of rows is zero:

unsigned int cases_rows = observations.cases.size();
unsigned int cases_cols = observations.cases[0].size();

I agree my method might not be needed but if you plan to drop it then we need to reorder so that the rows are checked before the columns are retrieved, i.e.:

unsigned int cases_rows = observations.cases.size();
ImportConsistencyCheck(scot_data_file, cases_rows, (nHealthBoards + 1), "rows");
unsigned int cases_cols = observations.cases[0].size();
ImportConsistencyCheck(scot_deaths_file, deaths_cols, nCasesDays, "columns");

instead.

[peter-t-fox]

Notwithstanding my comment above, I'd suggest that once you have checked that the data are valid once in the IO code, there's no reason to check again in the model code.