message: Fix a bug in the previous commit by returning Unimplemented.
diff: @@ -622,7 +622,7 @@ CudnnConvBackendConfig GetDefaultBackendConfig() {
  StatusOr<bool> RunOnInstruction(HloInstruction* conv) {
  CHECK_EQ(conv->opcode(), HloOpcode::kConvolution);
  - HloInstruction* custom_call = [&]() -> HloInstruction* {
  + HloInstruction* custom_call = [&]() -> StatusOr<HloInstruction*> {
  bool match;
  Window window;
  ConvolutionDimensionNumbers dnums;
  @@ -648,7 +648,7 @@ StatusOr<bool> RunOnInstruction(HloInstruction* conv) {
  if (primitive_util::IsIntegralType(
  conv->operand(0)->shape().element_type()) &&
  conv->shape().element_type() != F32) {
  - Unimplemented(
  + return Unimplemented(
  "The convolution instruction with integer inputs only allows "
  "float outputs. Insert a clamp instruction with range [-128, 127) "
  "followed by a convert "
  @@ -662,7 +662,7 @@ StatusOr<bool> RunOnInstruction(HloInstruction* conv) {
  }
  return nullptr;
  - }();
  + }().ValueOrDie();
  if (custom_call == nullptr) {
  return false;
  