a11y grap: explicit hwnd is authoritative in FindByMultiField

When grap pattern contains {hwnd:0x...} plus proc/title/cls hints, the hwnd is authoritative: IsWindow(hwnd) only, no AND-match on other fields. Fields drift across hot-swap rename, Chrome navigations, and dynamic dialog titles -- any drift used to drop the match to empty and caller fell through to closest-match enumeration, returning a wrong sibling popup on Hero4/HeroGlobal with 4+ #32770 dialogs.

Steps