Add swig.WaitForBlock(dec, sbn, err)

Make it wait for any block to be available and return its status.

FTR, potential error codes from compute() include:

* swig.Error_NONE -> source block (sbn) is ready
* swig.Error_EXITING -> underlying decoder has been deleted
* swig.Error_NEED_DATA -> source block (sbn) has reached end-of-input
  (as indicated by the caller) but still cannot be decoded.

Since we do not inject end-of-input, we will not get and do not have to
process NEED_DATA.

pkg/impl/libraptorq/swig/swig.swigcxx

@@ -1098,6 +1098,7 @@ public:
 %inline %{
 
 typedef RFC6330__v1::Impl::Encoder<unsigned char *, unsigned char *> BytesEncoder;
+typedef RFC6330__v1::Impl::Decoder<unsigned char *, unsigned char *> BytesDecoder;
 
 BytesEncoder *InitBytesEncoder(
  unsigned char *SLICEBEGIN, unsigned char *SLICEEND,
@@ -1110,4 +1111,10 @@ BytesEncoder *InitBytesEncoder(
  return enc;
 }
 
+void WaitForBlock(BytesDecoder *dec, uint8_t &sbn, RFC6330__v1::Error &err) {
+ auto result = dec->compute(RFC6330__v1::Compute::PARTIAL_ANY).get();
+ err = result.first;
+ sbn = result.second;
+}
+
 %}