Commit df3b0bd89f (Fix commandline state for custom completions with variable
overrides, 2022-01-26) made us push a transient command line for custom
completions based on a tautological null-pointer check ("var_assignments").
Commit 77aeb6a2a8 (Port execution, 2023-10-08) turned the null pointer into
a reference and replaced the check with "!ad.var_assignments.is_empty()".
This broke scenarios that relied on the transient commandline. In particular
the attached test cases rely on the transient commandline implicitly placing
the cursor at the end, irrespective of the cursor in the actual commandline.
I'm not sure if there is an easy way to identify these scenarios.
Let's restore historical behavior by always pushing the transient command line.
Fixes#11423
97641c7bf6