[asmjs] Return early when AsmWasmBuilder::Run fails.

R=bradnelson@chromium.org

Change-Id: Ifc492b2c2d361ebde5b143b599175b13860781ca
Reviewed-on: https://chromium-review.googlesource.com/448576
Commit-Queue: Brad Nelson <bradnelson@chromium.org>
Reviewed-by: Brad Nelson <bradnelson@chromium.org>
Cr-Commit-Position: refs/heads/master@{#43563}

src/asmjs/asm-wasm-builder.cc

@@ -2001,6 +2001,9 @@ AsmWasmBuilder::Result AsmWasmBuilder::Run(Handle<FixedArray>* foreign_args) {
                           info_->parse_info()->ast_value_factory(),
                           info_->script(), info_->literal(), &typer_);
   bool success = impl.Build();
+  if (!success) {
+    return {nullptr, nullptr, success};
+  }
   *foreign_args = impl.GetForeignArgs();
   ZoneBuffer* module_buffer = new (zone) ZoneBuffer(zone);
   impl.builder_->WriteTo(*module_buffer);