[wasm] Add the 'end' opcode at the end of the fuzzer input

Without the end opcode at the end of a function nearly every fuzzer
input would be invalid and test nothing.

R=titzer@chromium.org

Review-Url: https://codereview.chromium.org/2634943002
Cr-Commit-Position: refs/heads/master@{#42363}

test/fuzzer/wasm-call.cc

@@ -114,6 +114,8 @@ extern "C" int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size) {
         builder.AddFunction(sig_builder.Build());
     uint32_t code_size = static_cast<uint32_t>(size / num_functions);
     f->EmitCode(data, code_size);
+    uint8_t end_opcode = kExprEnd;
+    f->EmitCode(&end_opcode, 1);
     data += code_size;
     size -= code_size;
     if (fun == 0) {

test/fuzzer/wasm-code.cc

@@ -68,6 +68,8 @@ extern "C" int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size) {
   v8::internal::wasm::WasmFunctionBuilder* f =
       builder.AddFunction(sigs.i_iii());
   f->EmitCode(data, static_cast<uint32_t>(size));
+  uint8_t end_opcode = kExprEnd;
+  f->EmitCode(&end_opcode, 1);
   f->ExportAs(v8::internal::CStrVector("main"));
 
   ZoneBuffer buffer(&zone);