Segfault in pseudoWitnessSet calling PathTracker

Nobody has claimed this yet.

This was in an example for `isOnImage` in NumericalImplicitization:
```m2
-- -*- M2-comint -*- hash: 927871285

i1 : R = CC[x_(1,1)..x_(3,5)]; I = ideal 0_R;

o2 : Ideal of R

i3 : F = (minors(3, genericMatrix(R, 3, 5)))_*;

i4 : W = pseudoWitnessSet(F, I, Repeats => 2, Verbose => false);
-- SIGSEGV
-* stack trace, pid: 11133
0# stack_trace(std::ostream&, bool) at ../../Macaulay2/bin/main.cpp:124
1# segv_handler at ../../Macaulay2/bin/main.cpp:240
2# 0x00007F2A91E38FD0 in /lib/x86_64-linux-gnu/libc.so.6
3# SLP::concatenate(SLP const*) at ../../Macaulay2/e/NAG.cpp:382
4# PathTracker::make(Matrix const*) at ../../Macaulay2/e/NAG.cpp:1537
5# interface2_rawPathTracker at /home/runner/work/M2/M2/M2/Macaulay2/d/interface2.d:358
6# evaluate_evalraw at /home/runner/work/M2/M2/M2/Macaulay2/d/evaluate.d:1293
```
Full error: [_is__On__Image.errors.txt](https://github.com/Macaulay2/M2/files/5031529/_is__On__Image.errors.txt)

Reproduce the `pseudoWitnessSet` example from `isOnImage` in NumericalImplicitization and start with the stack trace in `NAG.cpp`, especially `SLP::concatenate` and `PathTracker::make`. Trace the call through `interface2_rawPathTracker`; done means the example no longer segfaults and the existing numerical behavior remains valid.

Written by the indexing model from the issue text.