[Interpreter] Do not write Ignition dispatch counters to file by default.

src/d8.cc

Index: src/d8.cc
diff --git a/src/d8.cc b/src/d8.cc
index 287c6a0f7a00f98c3c63f7942a9013ad30ea2626..9466ab7d3a727c2fe12d70ac977df0b0cac57f35 100644
--- a/src/d8.cc
+++ b/src/d8.cc
@@ -2495,7 +2495,8 @@ int Shell::Main(int argc, char* argv[]) {
     }
 
 #ifndef V8_SHARED
-    if (i::FLAG_ignition && i::FLAG_trace_ignition_dispatches) {
+    if (i::FLAG_ignition && i::FLAG_trace_ignition_dispatches &&
+        i::FLAG_trace_ignition_dispatches_output_file != nullptr) {
       WriteIgnitionDispatchCountersFile(isolate);
     }
 #endif