Check if a sharding custom call has a sharding before accessing the s…

…aid sharding object.

PiperOrigin-RevId: 676042171

xla/service/sharding_propagation.cc

@@ -1465,10 +1465,10 @@ absl::StatusOr<bool> ProcessShardingInstruction(
     for (auto it = instructions.rbegin(); it != instructions.rend(); ++it) {
       HloInstruction* instruction = *it;
       if (instruction->IsCustomCall("Sharding")) {
-        HloSharding original_sharding = instruction->sharding();
         TF_RET_CHECK(instruction->has_sharding())
             << "Sharding instruction must have a sharding attribute";
         VLOG(3) << "ProcessShardingInstruction: " << instruction->ToString();
+        HloSharding original_sharding = instruction->sharding();
 
         std::vector<int64_t> unspec_dims;
         TF_RETURN_IF_ERROR(sharding_op_util::ParseAttributes(