Disable inner scroll with viewport height zero

app/src/main/java/eu/faircode/email/WebViewEx.java

@@ -415,6 +415,8 @@ public class WebViewEx extends WebView implements DownloadListener, View.OnLongC
                 }
             }
         }
+        if (viewportHeight == 0)
+            intercept = false;
         getParent().requestDisallowInterceptTouchEvent(intercept || event.getPointerCount() > 1);
 
         lastX = event.getX();