Fix msvc compiling errors and warnings

Change-Id: I69916bb6390dd9275341d8cd3fae2d8961e1cae3
diff --git a/av1/decoder/obu.c b/av1/decoder/obu.c
index 67e9bb9..589b2c7 100644
--- a/av1/decoder/obu.c
+++ b/av1/decoder/obu.c
@@ -186,12 +186,11 @@
       case OBU_FRAME_HEADER:
         // Only decode first frame header received
         if (!frame_header_received) {
-          frame_header_size = obu_payload_size =
+          frame_header_size =
               read_frame_header_obu(pbi, data, data_end, p_data_end);
           frame_header_received = 1;
-        } else {
-          obu_payload_size = frame_header_size;
         }
+        obu_payload_size = frame_header_size;
         if (cm->show_existing_frame) frame_decoding_finished = 1;
         break;
       case OBU_TILE_GROUP: