remove unnecessary double check

lib/response.js

@@ -58,7 +58,7 @@ module.exports = function(request, response, result) {
   if (result.body) {
     // use Mojang's image hash if available
     // use crc32 as a hash function otherwise
-    var etag = result.body && result.hash && result.hash.substr(0, 10) || crc(result.body);
+    var etag = result.hash && result.hash.substr(0, 10) || crc(result.body);
     headers.Etag = "\"" + etag + "\"";
 
     // handle etag caching