isclock is not robust to non TimeDomain argument

[pitx-perf]

Describe the example

From #922
isclock(nothing) throws an error while it returned false previously.

Minimal Reproducible Example 👇
isclock(nothing)

Error & Stacktrace ⚠️

Not Working Environment (please complete the following information):

• Output of using Pkg; Pkg.status()

• Output of using Pkg; Pkg.status(; mode = PKGMODE_MANIFEST)

• Output of versioninfo()

Working Environment (please complete the following information):

• Output of using Pkg; Pkg.status()

• Output of using Pkg; Pkg.status(; mode = PKGMODE_MANIFEST)

• Output of versioninfo()

Additional context

Add any other context about the problem here.