LibWebView: Unbreak spawning WebContent process with valgrind

We now check if the WebContent is executable before passing it to
the valgrind wrapper. We can't rely on exec() to fail here, since it
will always succeed even when passing a bad WebContent path to valgrind.

Userland/Libraries/LibWebView/ViewImplementation.cpp

@@ -200,6 +200,10 @@ ErrorOr<NonnullRefPtr<WebView::WebContentClient>> ViewImplementation::launch_web
         ErrorOr<void> result;
         for (auto const& path : candidate_web_content_paths) {
             constexpr auto callgrind_prefix_length = 3;
+
+            if (Core::System::access(path, X_OK).is_error())
+                continue;
+
             auto arguments = Vector {
                 "valgrind"sv,
                 "--tool=callgrind"sv,