Use proper cached static image for unknown file

boards/models/attachment/viewers.py

@@ -1,4 +1,5 b''
 from django.template.defaultfilters import filesizeformat
+from django.templatetags.static import static
 
 
 class AbstractViewer:
@@ -19,10 +20,10 b' class AbstractViewer:'
 
     def get_view(self):
         return '<div class="image"><a href="{}">'\
-               '<img src="/static/images/file.png" width="200" height="150"/>'\
+               '<img src="{}" width="200" height="150"/>'\
                '</a>'\
                '<div class="image-metadata">{}, {}</div>'\
-               '</div>'.format(self.file.url, self.file_type,
+               '</div>'.format(self.file.url, static('images/file.png'), self.file_type,
                        filesizeformat(self.file.size))