fix: check unpack_callback_uint32 result (#666)

Similar to #665, just a return value check to propagate the error in
case one happens (instead of silently ignoring it).

Note that as opposed to the previous lines, we don't need to
`PyErr_SetString` since `unpack_callback_uint32` calls
`PyLong_FromSize_t` which itself should set whatever Python error is
relevant; we just need to make it clear to the caller that an error
occurred.

Author: KowalskiThomas

msgpack/unpack_container_header.h

@@ -45,7 +45,10 @@ static inline int unpack_container_header(unpack_context* ctx, const char* data,
         PyErr_SetString(PyExc_ValueError, "Unexpected type header on stream");
         return -1;
     }
-    unpack_callback_uint32(&ctx->user, size, &ctx->stack[0].obj);
+
+    if (unpack_callback_uint32(&ctx->user, size, &ctx->stack[0].obj) < 0)
+        return -1;
+
     return 1;
 }