A few more fixes.

upb/pb/decoder.h

@@ -117,6 +117,7 @@ void upb_pbdecoder_reset(upb_pbdecoder *d);
  * decoded data to its output sink. */
 class upb::pb::DecoderPtr {
  public:
+  DecoderPtr() : ptr_(nullptr) {}
   DecoderPtr(upb_pbdecoder* ptr) : ptr_(ptr) {}
 
   upb_pbdecoder* ptr() { return ptr_; }

upb/sink.h

@@ -503,7 +503,7 @@ bool upb_bufsrc_putbuf(const char *buf, size_t len, upb_bytessink sink);
 
 namespace upb {
 template <class T> bool PutBuffer(const T& str, BytesSink sink) {
-  return upb_bufsrc_putbuf(str.c_str(), str.size(), sink.sink());
+  return upb_bufsrc_putbuf(str.data(), str.size(), sink.sink());
 }
 }