FIX Skip md5-ing the whole contents of a stream for etags

src/Control/Middleware/ChangeDetectionMiddleware.php

@@ -4,6 +4,7 @@ namespace SilverStripe\Control\Middleware;
 
 use SilverStripe\Control\HTTPRequest;
 use SilverStripe\Control\HTTPResponse;
+use SilverStripe\Control\HTTPStreamResponse;
 use SilverStripe\Core\Injector\Injectable;
 
 /**
@@ -69,6 +70,11 @@ class ChangeDetectionMiddleware implements HTTPMiddleware
             return $etag;
         }
 
+        // Skip parsing the whole body of a stream
+        if ($response instanceof HTTPStreamResponse) {
+            return false;
+        }
+
         // Generate etag from body
         return sprintf('"%s"', md5($response->getBody()));
     }