inspector: check if connected before waiting

Fixes: https://github.com/nodejs/node/issues/10093
PR-URL: https://github.com/nodejs/node/pull/10094
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>

src/inspector_agent.cc

@@ -548,10 +548,12 @@ bool AgentImpl::IsStarted() {
 }
 
 void AgentImpl::WaitForDisconnect() {
-  shutting_down_ = true;
-  fprintf(stderr, "Waiting for the debugger to disconnect...\n");
-  fflush(stderr);
-  inspector_->runMessageLoopOnPause(0);
+  if (state_ == State::kConnected) {
+    shutting_down_ = true;
+    fprintf(stderr, "Waiting for the debugger to disconnect...\n");
+    fflush(stderr);
+    inspector_->runMessageLoopOnPause(0);
+  }
 }
 
 #define READONLY_PROPERTY(obj, str, var)                                      \

test/inspector/test-inspector-stops-no-file.js

@@ -0,0 +1,15 @@
+'use strict';
+require('../common');
+const spawn = require('child_process').spawn;
+
+const child = spawn(process.execPath,
+                    [ '--inspect', 'no-such-script.js' ],
+                    { 'stdio': 'inherit' });
+
+function signalHandler(value) {
+  child.kill();
+  process.exit(1);
+}
+
+process.on('SIGINT', signalHandler);
+process.on('SIGTERM', signalHandler);