minor cleanup to previous commit from code review

app/models/optimized_image.rb

@@ -43,7 +43,7 @@ class OptimizedImage < ActiveRecord::Base
 
     # correct bad thumbnail if needed
     if thumbnail && thumbnail.url.blank?
-      thumbnail.destroy
+      thumbnail.destroy!
       thumbnail = nil
     end
 

lib/distributed_mutex.rb

@@ -22,10 +22,12 @@ class DistributedMutex
 
     while !try_to_get_lock
       sleep 0.001
-      attempts += 1
       # in readonly we will never be able to get a lock
-      if @using_global_redis && attempts > CHECK_READONLY_ATTEMPT
-        raise Discourse::ReadOnly
+      if @using_global_redis
+        attempts += 1
+        if attempts > CHECK_READONLY_ATTEMPT
+          raise Discourse::ReadOnly
+        end
       end
     end