Check for soup body in `remove_site_blocks` (#651)

Fixes error with `remove_site_blocks` in the Images tab

app/filter.py

@@ -123,7 +123,7 @@ class Filter:
         return soup
 
     def remove_site_blocks(self, soup) -> None:
-        if not self.config.block:
+        if not self.config.block or not soup.body:
             return
         search_string = ' '.join(['-site:' +
                                  _ for _ in self.config.block.split(',')])