Wrap getAFIs and getMIs calls in permuteOnce.mgcfa and permuteOnce.mimic with tryCatch (closes #159)

[Shotgunosine]

When getAFIs (calling lavaan::fitMeasures) or getMIs (calling lavaan::lavTestScore) errors during a permutation iteration — for example due to LAPACK dgesdd failures on numerically pathological score-test matrices, see Reference-LAPACK/lapack#672 — the unhandled error kills the worker. Under parallelType = "multicore" this causes mclapply to return a try-error for that permutation, which then crashes the aggregation at line ~990 with Error in x$AFI : $ operator is invalid for atomic vectors.

The fix wraps both calls in tryCatch with the same NA fallback that the function already uses for the sparse/nonconv branch (lines 1404–1410), so a single bad permutation contributes NA to the null distribution rather than terminating the entire call. I applied the same change to permuteOnce.mimic for consistency.

Note that I didn't add a new counter for something like n.LapackFail, so the n.nonConverged counter will be under-counting the true number of failures. I kept this initial proposed fix as narrow in scope as possible, but I can try to add an additional failure counter if you'd like.