main: always delete CefCache before starting CEF

It seems CEF can't be trusted to store valid cache between shutdowns or
system updates, which leads to infrequent reports of SKIA shader
compilation errors, the only fix for which is to delete CefCache or
GPUCache. If that's the case, I won't let it store anything at all. This
doesn't appear to affect startup time.

src/main.cxx

@@ -92,6 +92,14 @@ int BoltRunBrowserProcess(CefMainArgs main_args, CefRefPtr<Browser::App> cef_app
 	// Give CEF a place to put its cache stuff - default location is next to the exe which is not OK
 	std::filesystem::path cef_cache_path = data_dir;
 	cef_cache_path.append("CefCache");
+	if (std::filesystem::exists(cef_cache_path)) {
+		std::error_code err;
+		std::filesystem::remove_all(cef_cache_path, err);
+		if (err.value()) {
+			fmt::print("Can't delete CefCache: error {} '{}'\n", err.value(), err.message());
+			return err.value();
+		}
+	}
 	std::filesystem::create_directories(cef_cache_path);
 #if defined(_WIN32)
 	const wchar_t* cache_path = cef_cache_path.c_str();