always output a png

diff --git a/lib/private/preview.php b/lib/private/preview.php
index 74051fbc2a3dab8d772e8ce81fcff879986aa960..70bfdb6e70ace9554ae8164a1c0c29e3677ff03f 100755 (executable)
--- a/lib/private/preview.php
+++ b/lib/private/preview.php
@@ -463,7 +463,7 @@ class Preview {
                if (is_null($this->preview)) {
                        $this->getPreview();
                }
-               $this->preview->show();
+               $this->preview->show('image/png');
                return;
        }