Skip SPIR-V validation when not generating SPIR-V

Otherwise the sample app crashes when using --dawn-validation with a
non-SPIR-V output format.

Change-Id: Ic6e03e758747602d15f3a1d5b9d9cefee1aad527
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/41120
Commit-Queue: dan sinclair <dsinclair@chromium.org>
Auto-Submit: James Price <jrprice@google.com>
Reviewed-by: dan sinclair <dsinclair@chromium.org>
diff --git a/samples/main.cc b/samples/main.cc
index fe7ee56..3c6c5b5 100644
--- a/samples/main.cc
+++ b/samples/main.cc
@@ -593,7 +593,8 @@
   bool dawn_validation_failed = false;
   std::ostringstream stream;
 
-  if (options.dawn_validation) {
+  if (options.dawn_validation &&
+      (options.format == Format::kSpvAsm || options.format == Format::kSpirv)) {
     // Use Vulkan 1.1, since this is what Tint, internally, uses.
     spvtools::SpirvTools tools(SPV_ENV_VULKAN_1_1);
     tools.SetMessageConsumer([&stream](spv_message_level_t, const char*,