Failsafe on Redis error replies in RedisCacheStoreProxy.

RedisCacheStoreProxy will blow up when RedisCacheStore raises a
CommandError exception. In fact, by default the proxied store only
handles BaseConnectionError exceptions, but will let bubble up any other
type of exception from the underlying client.

This pull request uses the same approach from RedisProxy, where store
operations are wrapped in a `rescuing` block that rescues and ignores
BaseError exceptions (the most generic exception class that can be
raised by the Redis client).

lib/rack/attack/store_proxy/redis_cache_store_proxy.rb

@@ -15,17 +15,33 @@ module Rack
           #
           # So in order to workaround this we use RedisCacheStore#write (which sets expiration) to initialize
           # the counter. After that we continue using the original RedisCacheStore#increment.
-          if options[:expires_in] && !read(name)
-            write(name, amount, options)
+          rescuing do
+            if options[:expires_in] && !read(name)
+              write(name, amount, options)
 
-            amount
-          else
-            super
+              amount
+            else
+              super
+            end
           end
         end
 
+        def read(*_args)
+          rescuing { super }
+        end
+
         def write(name, value, options = {})
-          super(name, value, options.merge!(raw: true))
+          rescuing do
+            super(name, value, options.merge!(raw: true))
+          end
+        end
+
+        private
+
+        def rescuing
+          yield
+        rescue Redis::BaseError
+          nil
         end
       end
     end