Check Python ByteBuffer reader init status

src/python/grpcio/grpc/_cython/_cygrpc/grpc.pxi

@@ -132,8 +132,8 @@ cdef extern from "grpc/_cython/loader.h":
   size_t grpc_byte_buffer_length(grpc_byte_buffer *bb) nogil
   void grpc_byte_buffer_destroy(grpc_byte_buffer *byte_buffer) nogil
 
-  void grpc_byte_buffer_reader_init(grpc_byte_buffer_reader *reader,
+  int grpc_byte_buffer_reader_init(grpc_byte_buffer_reader *reader,
-                                    grpc_byte_buffer *buffer) nogil
+                                   grpc_byte_buffer *buffer) nogil
   int grpc_byte_buffer_reader_next(grpc_byte_buffer_reader *reader,
                                    gpr_slice *slice) nogil
   void grpc_byte_buffer_reader_destroy(grpc_byte_buffer_reader *reader) nogil

src/python/grpcio/grpc/_cython/_cygrpc/records.pyx.pxi

@@ -252,9 +252,13 @@ cdef class ByteBuffer:
     cdef gpr_slice data_slice
     cdef size_t data_slice_length
     cdef void *data_slice_pointer
+    cdef bint reader_status
     if self.c_byte_buffer != NULL:
       with nogil:
-        grpc_byte_buffer_reader_init(&reader, self.c_byte_buffer)
+        reader_status = grpc_byte_buffer_reader_init(
+            &reader, self.c_byte_buffer)
+      if not reader_status:
+        return None
       result = bytearray()
       with nogil:
         while grpc_byte_buffer_reader_next(&reader, &data_slice):