[bazel] bazelisk.sh unbound variable error when invoked with dvsim.py to run TLT

[gdessouky]

Description

dvsim.py invokes bazelisk.sh when running top-level-tests. When exercising a TLT, e.g. /util/dvsim/dvsim.py hw/top_earlgrey/dv/chip_sim_cfg.hjson -i chip_sw_hmac_smoketest, (or bazelisk.sh alone) this errors out with

./bazelisk.sh: line 172: pre_cmd_args[@]: unbound variable

I suspect this is a side effect of this last commit 4d88b95, since once I undo it, the test run proceeds further.

When cross-checking with @andreaskurth it works fine at their end (GNU bash, version 5.1.16(1)-release (x86_64-pc-linux-gnu) and not at my end (GNU bash, version 4.2.46(2)-release (x86_64-redhat-linux-gnu)), until I revert that last commit.

[jwnrt]

Thanks for flagging, I didn't expect these changes to break in an older Bash version.

I could reproduce this in Bash 4.2 but I'm not sure why. I've opened #21826 as a workaround but it doesn't fix the actual issue. Would be great to get some help from somebody who knows a bit more about Bash, but I'm not sure who that could be.