Fix error handling in vp9_pack_bitstream()

In multi-threaded scenario, when the bitstream
buffer allocated is insufficient, the main thread
called 'longjmp' without waiting for the completion
of workers. In this patch, 'longjmp' is called by
the main thread after joining other worker threads.

This resolves the assertion failure as reported in
Bug: webm:1847

Bug: webm:1844

Change-Id: I399c76087b65e7b8d9a9fa4f12d784408243d648

vp9/encoder/vp9_bitstream.c

@@ -996,6 +996,7 @@ static size_t encode_tiles_mt(VP9_COMP *cpi, uint8_t *data_ptr,
   const int num_workers = cpi->num_workers;
   size_t total_size = 0;
   int tile_col = 0;
+  int error = 0;
 
   const size_t buffer_alloc_size = encode_tiles_buffer_alloc_size(cpi);
   if (!cpi->vp9_bitstream_worker_data ||
@@ -1049,9 +1050,10 @@ static size_t encode_tiles_mt(VP9_COMP *cpi, uint8_t *data_ptr,
       int k;
 
       if (!winterface->sync(worker)) {
-        vpx_internal_error(&cm->error, VPX_CODEC_ERROR,
-                           "encode_tiles_mt: worker had error");
+        error = 1;
+        continue;
       }
+
       tile_size = data->bit_writer.pos;
 
       // Aggregate per-thread bitstream stats.
@@ -1064,21 +1066,25 @@ static size_t encode_tiles_mt(VP9_COMP *cpi, uint8_t *data_ptr,
       // Prefix the size of the tile on all but the last.
       if (tile_col != tile_cols || j < i - 1) {
         if (data_size - total_size < 4) {
-          vpx_internal_error(&cm->error, VPX_CODEC_ERROR,
-                             "encode_tiles_mt: output buffer full");
+          error = 1;
+          continue;
         }
         mem_put_be32(data_ptr + total_size, tile_size);
         total_size += 4;
       }
       if (j > 0) {
         if (data_size - total_size < tile_size) {
-          vpx_internal_error(&cm->error, VPX_CODEC_ERROR,
-                             "encode_tiles_mt: output buffer full");
+          error = 1;
+          continue;
         }
         memcpy(data_ptr + total_size, data->dest, tile_size);
       }
       total_size += tile_size;
     }
+    if (error) {
+      vpx_internal_error(&cm->error, VPX_CODEC_ERROR,
+                         "encode_tiles_mt: output buffer full");
+    }
   }
   return total_size;
 }