Disable sliding sync proxy check for native support mode (#11936)

Signed-off-by: Michael Telatynski <7t3chguy@gmail.com>

src/components/views/dialogs/SlidingSyncOptionsDialog.tsx

@@ -86,8 +86,9 @@ export const SlidingSyncOptionsDialog: React.FC<{ onFinished(enabled: boolean):
 
     const validProxy = withValidation<undefined, { error?: unknown }>({
         async deriveData({ value }): Promise<{ error?: unknown }> {
+            if (!value) return {};
             try {
-                await proxyHealthCheck(value!, MatrixClientPeg.safeGet().baseUrl);
+                await proxyHealthCheck(value, MatrixClientPeg.safeGet().baseUrl);
                 return {};
             } catch (error) {
                 return { error };