Don't continue with an invalid iterator

Bug: 112181526
Test: build
Change-Id: Ifa3bfa60d2303a294ee842de6729a0c911b42f88
(cherry picked from commit cf6899a77b583d37597c07e6a542422cb9821964)
diff --git a/vda/v4l2_slice_video_decode_accelerator.cc b/vda/v4l2_slice_video_decode_accelerator.cc
index 98e5915..2d81020 100644
--- a/vda/v4l2_slice_video_decode_accelerator.cc
+++ b/vda/v4l2_slice_video_decode_accelerator.cc
@@ -997,6 +997,7 @@
     if (it == surfaces_at_device_.end()) {
       DLOGF(ERROR) << "Got invalid surface from device.";
       NOTIFY_ERROR(PLATFORM_FAILURE);
+      return;
     }
 
     it->second->SetDecoded();