Bugfixes to upb_stdio and upb_decoder.

stream/upb_decoder.c

@@ -91,10 +91,10 @@ static bool upb_decoder_nextbuf(upb_decoder *d)
 
   // Recycle old buffer.
   if(d->buf) {
-    d->buf = upb_string_tryrecycle(d->buf);
     d->buf_offset -= upb_string_len(d->buf);
     d->buf_stream_offset += upb_string_len(d->buf);
   }
+  d->buf = upb_string_tryrecycle(d->buf);
 
   // Pull next buffer.
   if(upb_bytesrc_get(d->bytesrc, d->buf, UPB_MAX_ENCODED_SIZE)) {
@@ -569,6 +569,7 @@ void upb_decoder_reset(upb_decoder *d, upb_bytesrc *bytesrc)
   // to UINT32_MAX so it doesn't equal UPB_GROUP_END_OFFSET.
   d->top->end_offset = UINT32_MAX - 1;
   d->bytesrc = bytesrc;
+  d->field = NULL;
   d->buf = NULL;
   d->buf_bytesleft = 0;
   d->buf_stream_offset = 0;

stream/upb_stdio.c

@@ -53,7 +53,7 @@ bool upb_stdio_append(upb_bytesrc *src, upb_string *str, upb_strlen_t len) {
 }
 
 int32_t upb_stdio_put(upb_bytesink *sink, upb_string *str) {
-  upb_stdio *stdio = (upb_stdio*)sink - offsetof(upb_stdio, bytesink);
+  upb_stdio *stdio = (upb_stdio*)((char*)sink - offsetof(upb_stdio, bytesink));
   upb_strlen_t len = upb_string_len(str);
   size_t written = fwrite(upb_string_getrobuf(str), 1, len, stdio->file);
   if(written < len) {