Fix warning about unininitialized values in finish_integrate_fast

[masterleinad]

Fixes #16012. Alternative to #16018.

[masterleinad]

/rebuild

[masterleinad]

@bergbauer FYI This fixes the warning for me.

[bergbauer]

Does changing from n_q_points to n_q_batches here

dealii/include/deal.II/matrix_free/fe_point_evaluation.h

Line 2644 in 46f530f

if (n_q_points == 0 || // no evaluation points provided

also fix the warning for you? Then we would not need an additional runtime if.

[masterleinad]

Does changing from n_q_points to n_q_batches [...] also fix the warning for you? Then we would not need an additional runtime if.

No, that's not enough. Since the stacktrace has include/deal.II/matrix_free/fe_point_evaluation.h:2548 as the last node, it seems the compiler is assuming that the function could be called from something else than FEPointEvaluation<n_components_, dim, spacedim, Number>::do_integrate().

[kronbichler]

I guess we could go with this patch, if you don't see a change in performance @bergbauer?

[kronbichler]

I went with the other PR due to the additional warning of gcc-13, let us keep this PR in mind in case we discover a similar issue in the future, thanks for the effort @masterleinad!