ChooseRichDocumentsTemplate: avoid IOOBE if there is no dot in field

Signed-off-by: Álvaro Brey <alvaro.brey@nextcloud.com>

app/src/main/java/com/owncloud/android/ui/dialog/ChooseRichDocumentsTemplateDialogFragment.java

@@ -249,7 +249,11 @@ public class ChooseRichDocumentsTemplateDialogFragment extends DialogFragment im
         if (name.isEmpty() || name.equalsIgnoreCase(DOT + template.getExtension())) {
             binding.filename.setText(String.format("%s.%s", template.getName(), template.getExtension()));
         }
-        binding.filename.setSelection(binding.filename.getText().toString().lastIndexOf('.'));
+
+        final int dotIndex = binding.filename.getText().toString().lastIndexOf('.');
+        if (dotIndex >= 0) {
+            binding.filename.setSelection(dotIndex);
+        }
     }
 
     private void checkEnablingCreateButton() {