[hotfix] printing images

frappe/templates/print_formats/standard_macros.html

@@ -89,7 +89,7 @@ data-fieldname="{{ df.fieldname }}" data-fieldtype="{{ df.fieldtype }}"
 	{% elif df.fieldtype=="Image" %}
 		<img src="{{ doc[doc.meta.get_field(df.fieldname).options] }}" class="img-responsive">
 	{% elif df.fieldtype in ("Attach", "Attach Image") and doc[df.fieldname]
-		and guess_mimetype(doc[df.fieldname])[0].startswith("image/") %}
+		and (guess_mimetype(doc[df.fieldname])[0] or "").startswith("image/") %}
 		<img src="{{ doc[df.fieldname] }}" class="img-responsive">
     {% elif df.fieldtype=="HTML" %}
         {{ frappe.render_template(df.options, {"doc":doc}) }}