os/exec: Cmd.{Run,Start} should fail if Cmd.Path is unset [1.18 backport]

[gopherbot]

@rolandshoemaker requested issue #52574 to be considered for backport to the next 1.18 minor release.

@gopherbot please open backport issues, this is a minor security issue.

[toothrot]

Approved. This is a serious issue with no workaround. @rolandshoemaker Does this need security text?

[gopherbot]

Change https://go.dev/cl/408577 mentions this issue: [release-branch.go1.18] os/exec: return clear error for missing cmd.Path

[rolandshoemaker]

@toothrot Yup, will follow-up OOB.

[gopherbot]

Closed by merging 6c65a4a to release-branch.go1.18.