Use a reference instead of a nonnull pointer in systemFallbackForCharacters()
Pull request: https://github.com/WebKit/WebKit/pull/2026
Committed 252092@main (4632cc255c59): <https://commits.webkit.org/252092@main> Reviewed commits have been landed. Closing PR #2026 and removing active labels.
<rdar://problem/96334872>