Cherry-pick 2aaac53. rdar://126706870

    Add page null check under [WKWebProcessPlugInFrame _browserContextController]
    https://bugs.webkit.org/show_bug.cgi?id=271174
    rdar://122276358

    Reviewed by Sihui Liu.

    Add page null check under [WKWebProcessPlugInFrame _browserContextController] to address
    some crashes in the wild.

    * Source/WebKit/WebProcess/InjectedBundle/API/Cocoa/WKWebProcessPlugInFrame.mm:
    (-[WKWebProcessPlugInFrame _browserContextController]):

    Canonical link: https://commits.webkit.org/276318@main

Source/WebKit/WebProcess/InjectedBundle/API/Cocoa/WKWebProcessPlugInFrame.mm

@@ -117,6 +117,8 @@ - (JSValue *)jsRangeForRangeHandle:(WKWebProcessPlugInRangeHandle *)rangeHandle
 
 - (WKWebProcessPlugInBrowserContextController *)_browserContextController
 {
+    if (!_frame->page())
+        return nil;
     return WebKit::wrapper(*_frame->page());
 }