Cherry-pick 7900c68. rdar://122974809

    Exception in WebKit::WebExtensionTab::processes().
    https://webkit.org/b/269409
    rdar://122974809

    Reviewed by Jeff Miller and Brian Weinstein.

    When mainWebView() is nil, we need to be careful. Use [NSArray arrayWithObjects:]
    instead of [NSArray arrayWithObject:] since that will make a zero item array
    if the web view is nil, instead of throwing an exception.

    * Source/WebKit/UIProcess/Extensions/Cocoa/WebExtensionTabCocoa.mm:
    (WebKit::WebExtensionTab::processes const):

    Canonical link: https://commits.webkit.org/274669@main

Canonical link: https://commits.webkit.org/274594.3@safari-7619.1.4-branch

Source/WebKit/UIProcess/Extensions/Cocoa/WebExtensionTabCocoa.mm

@@ -893,7 +893,8 @@
     if (!isValid())
         return { };
 
-    auto *webViews = mainWebViewOnly == MainWebViewOnly::Yes ? [NSArray arrayWithObject:mainWebView()] : this->webViews();
+    // This approach is nil-safe, unlike using @[ mainWebView() ] or [NSArray arrayWithObject:].
+    auto *webViews = mainWebViewOnly == MainWebViewOnly::Yes ? [NSArray arrayWithObjects:mainWebView(), nil] : this->webViews();
 
     WebProcessProxySet result;
     for (WKWebView *webView in webViews) {