Add nullptr check for ProcessLauncher client in ProcessLauncher::finishLaunchingProcess.
<rdar://problem/122995875>
Pull request: https://github.com/WebKit/WebKit/pull/24784
Committed 275047@main (9ff5a32ea773): <https://commits.webkit.org/275047@main> Reviewed commits have been landed. Closing PR #24784 and removing active labels.
Re-opening for pull request https://github.com/WebKit/WebKit/pull/24822
*** Bug 269977 has been marked as a duplicate of this bug. ***