A missing or label-less header must still print and exit 0. Returning 1
would hand control back to the caller's body, which for upgrade(1) is a
full system upgrade.
Both fixtures reach the renderer's bottom `count $out -eq 0` fallback,
not the unreadable-source branch. Mutating that fallback to `return 1`
turns the test red with:
headerless executed its body despite --help
malformed executed its body despite --help
The mutation was reverted before this commit.
rootiest
b424b26700