Crash in getSequenceOfSmallIntegers in util.d

[mahrud]

From an example of superTrace in SuperLinearAlgebra that ran here:

-- -*- M2-comint -*- hash: 325525533

i1 : R1 = QQ[x_0..x_3];

i2 : R2 = QQ[z_0..z_2];

i3 : R = superRing(R1, R2);
-- SIGSEGV
-* stack trace, pid: 14966
 0# stack_trace(std::ostream&, bool) at ../../Macaulay2/bin/main.cpp:124
 1# segv_handler at ../../Macaulay2/bin/main.cpp:240
 2# 0x00007F8656BD3210 in /lib/x86_64-linux-gnu/libc.so.6
 3# GC_malloc_kind in /lib/x86_64-linux-gnu/libgc.so.1
 4# util_getSequenceOfSmallIntegers at /home/runner/work/M2/M2/M2/Macaulay2/d/util.d:89
 5# interface_rawSubmatrix at /home/runner/work/M2/M2/M2/Macaulay2/d/interface.dd:2675