When polling, raise if an error is returned (#142)

Previously, if an error from the API was returned while polling for updates on a file, it would continue polling. I updated it so that it raises a RequestError if the API returns an error status. If not, it raises a RetryError, which is swallowed by the retry gem's `with_retries` block.

Example of an error that led to continued polling:

```
{"status":"error","error":"File validation error: Uploading of these file types is not allowed.","error_code":"DownloadFileValidationFailedError"}
```

lib/uploadcare.rb

@@ -6,6 +6,7 @@
 # Exceptions
 require 'exception/throttle_error'
 require 'exception/request_error'
+require 'exception/retry_error'
 
 # Entities
 require 'entity/entity'

lib/uploadcare/client/uploader_client.rb

@@ -75,12 +75,22 @@ def post(args = {})
       def poll_upload_response(token)
         with_retries(max_tries: Uploadcare.config.max_request_tries,
                      base_sleep_seconds: Uploadcare.config.base_request_sleep,
-                     max_sleep_seconds: Uploadcare.config.max_request_sleep) do
+                     max_sleep_seconds: Uploadcare.config.max_request_sleep,
+                     rescue: RetryError) do
           response = get_upload_from_url_status(token)
-          raise RequestError if %w[progress waiting unknown].include?(response.success[:status])
+          handle_polling_response(response)
+        end
+      end
 
-          response
+      def handle_polling_response(response)
+        case response.success[:status]
+        when 'error'
+          raise RequestError, response.success[:error]
+        when 'progress', 'waiting', 'unknown'
+          raise RetryError, response.success[:error]
         end
+
+        response
       end
 
       # Prepares body for upload_many method

lib/uploadcare/exception/request_error.rb

@@ -3,7 +3,6 @@
 module Uploadcare
   module Exception
     # Standard error for invalid API responses
-    class RequestError < StandardError
-    end
+    class RequestError < StandardError; end
   end
 end

lib/uploadcare/exception/retry_error.rb

@@ -0,0 +1,8 @@
+# frozen_string_literal: true
+
+module Uploadcare
+  module Exception
+    # Standard error to raise when needing to retry a request
+    class RetryError < StandardError; end
+  end
+end