do not exit tool if fuchsia workflow fails (#26589)

packages/flutter_tools/lib/src/fuchsia/fuchsia_device.dart

@@ -115,6 +115,9 @@ class FuchsiaDevices extends PollingDeviceDiscovery {
       return <Device>[];
     }
     final String text = await fuchsiaSdk.listDevices();
+    if (text == null) {
+      return <Device>[];
+    }
     final List<FuchsiaDevice> devices = parseListDevices(text);
     return devices;
   }

packages/flutter_tools/lib/src/fuchsia/fuchsia_sdk.dart

@@ -5,12 +5,12 @@
 import 'dart:async';
 import 'dart:convert';
 
-import '../base/common.dart';
 import '../base/context.dart';
 import '../base/file_system.dart';
 import '../base/io.dart';
 import '../base/process.dart';
 import '../base/process_manager.dart';
+import '../globals.dart';
 
 /// The [FuchsiaSdk] instance.
 FuchsiaSdk get fuchsiaSdk => context[FuchsiaSdk];
@@ -33,8 +33,8 @@ class FuchsiaSdk {
       final String path = fuchsiaArtifacts.devFinder.absolute.path;
       final RunResult process = await runAsync(<String>[path, 'list', '-full']);
       return process.stdout.trim();
-    } on ArgumentError catch (exception) {
-      throwToolExit('$exception');
+    } catch (exception) {
+      printTrace('$exception');
     }
     return null;
   }
@@ -57,8 +57,8 @@ class FuchsiaSdk {
         controller.addStream(process.stdout.transform(utf8.decoder).transform(const LineSplitter()));
       });
       return controller.stream;
-    } on ArgumentError catch (exception) {
-      throwToolExit('$exception');
+    } catch (exception) {
+      printTrace('$exception');
     }
     return null;
   }