gracefully handle nil media_type

closes EVAL-4415
flag=speedgrader_studio_media_capture

Fixes a bug where the VideoCaptionService would raise an errror if the
media_type was nil. Now, it'll gracefully handle that case and set the
auto_caption_status on the media object to failed_initial_validation.

Test Plan:
- specs pass

Change-Id: Ie148c1ab43f87341bf761bd18658e1872d9dcb59
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/353784
Reviewed-by: Cameron Ray <cameron.ray@instructure.com>
Tested-by: Service Cloud Jenkins <svc.cloudjenkins@instructure.com>
QA-Review: Spencer Olson <solson@instructure.com>
Product-Review: Cameron Ray <cameron.ray@instructure.com>

app/services/video_caption_service.rb

@@ -52,7 +52,7 @@ class VideoCaptionService < ApplicationService
   def pass_initial_checks
     return false unless config["app-host"].present?
     return false unless auth_token.present?
-    return false unless @type.include?("video")
+    return false unless @type&.include?("video")
     return false unless @media_id
     return false if @media_object.media_tracks.where(kind: "subtitles").exists?
     return false if url.nil?

spec/services/video_caption_service_spec.rb

@@ -21,6 +21,20 @@ RSpec.describe VideoCaptionService, type: :service do
   let(:service) { VideoCaptionService.new(media_object, skip_polling: true) }
 
   describe "#call" do
+    context "when media type is nil" do
+      it "handles the request gracefully and sets status to failed_initial_validation" do
+        media_object.update!(media_type: nil)
+        allow(service).to receive_messages(
+          config: { "app-host" => "https://example.com" },
+          auth_token: "token"
+        )
+
+        expect { service.call }.to change {
+          media_object.reload.auto_caption_status
+        }.from(nil).to("failed_initial_validation")
+      end
+    end
+
     context "when media type is video and media id is present" do
       before do
         allow(service).to receive_messages(