Added fail-safe

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

@@ -959,6 +959,7 @@ public class StyleHelper {
     static void markAsInserted(Editable text, int start, int end) {
         for (InsertedSpan span : text.getSpans(0, text.length(), InsertedSpan.class))
             text.removeSpan(span);
+        if (start >= 0 && start < end && end <= text.length())
             text.setSpan(new InsertedSpan(), start, end, Spannable.SPAN_EXCLUSIVE_EXCLUSIVE);
     }