[wasm] Fix disassembly of wasm-stub call while on-heap.

R=clemensh@chromium.org
BUG=v8:8263

Change-Id: I6149cc6b353d4676a4b9170c906fe37822020217
Reviewed-on: https://chromium-review.googlesource.com/c/1267941Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Commit-Queue: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56435}

src/disassembler.cc

@@ -252,7 +252,8 @@ static void PrintRelocInfo(StringBuilder* out, Isolate* isolate,
     } else {
       out->AddFormatted(" %s", Code::Kind2String(kind));
     }
-  } else if (RelocInfo::IsWasmStubCall(rmode)) {
+  } else if (RelocInfo::IsWasmStubCall(rmode) && !isolate) {
+    // Host is isolate-independent, try wasm native module instead.
     wasm::WasmCode* code = host.as_wasm_code()->native_module()->Lookup(
         relocinfo->wasm_stub_call_address());
     out->AddFormatted("    ;; wasm stub: %s", code->GetRuntimeStubName());