Shutting down daemon process if build_runner throws. (#4274)

Consecutive execution of `webdev serve` when `build_runner` throws was causing an errant VM process to hold onto websocket connections, resulting in:
```
WebSocketChannelException: SocketException: Connection refused (OS Error: Connection refused, errno = 61), address = localhost, port = XXXXX
```

Author: Markzipan

build_daemon/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 4.1.1
+
+- Bug fix: daemon process shuts down on internal error.
+
 ## 4.1.0
 
 - Bug fix: resolve symlinks when identifying workspaces, so symlinks can't

build_daemon/lib/client.dart

@@ -195,7 +195,12 @@ class BuildDaemonClient {
       includeParentEnvironment: includeParentEnvironment,
     );
 
-    await _handleDaemonStartup(process, logHandler);
+    try {
+      await _handleDaemonStartup(process, logHandler);
+    } catch (_) {
+      process.kill();
+      rethrow;
+    }
 
     return connectUnchecked(
       workingDirectory,

build_daemon/pubspec.yaml

@@ -1,5 +1,5 @@
 name: build_daemon
-version:  4.1.0
+version:  4.1.1
 description: A daemon for running Dart builds.
 repository: https://github.com/dart-lang/build/tree/master/build_daemon
 resolution: workspace