fix(ui): only start ui if there are tasks to run (#8703)
### Description
Previously we would crash if a user provided a filter that matched zero
tasks. We should avoid starting the UI at all in this situation.
### Testing Instructions
Before
```
[0 olszewski@chriss-mbp] /Users/olszewski/code/vercel/turborepo $ turbo_dev build --filter='./packages/'
Oops! Turbo has crashed.
A report has been written to /var/folders/3m/rxkycvgs5jgfvs0k9xcgp6km0000gn/T/report-5f29ea16-7ad7-428f-ac6a-28607b4eb04a.toml
Please open an issue at https://github.com/vercel/turbo/issues/new/choose and include this file
No tasks were executed as part of this run.
Tasks: 0 successful, 0 total
Cached: 0 cached, 0 total
Time:
402ms
Run: https://vercel.com/teams/vercel/repos/turbo-monorepo/runs/space_run_xgkHsGl7exeeqKI3RfLZq2iK
Oops! Turbo has crashed.
A report has been written to /var/folders/3m/rxkycvgs5jgfvs0k9xcgp6km0000gn/T/report-1449aa95-2984-4859-9028-c2ddb899fbaf.toml
Please open an issue at https://github.com/vercel/turbo/issues/new/choose and include this file
⠁
> ...Finishing writing to cache... WARNING could not start shutdown, exiting
```
After
```
[0 olszewski@chriss-mbp] /Users/olszewski/code/vercel/turborepo $ turbo_dev build --filter='./packages/'
WARNING No locally installed `turbo` found. Using version: 2.0.7-canary.0.
• Packages in scope:
• Running build in 0 packages
• Remote caching enabled
No tasks were executed as part of this run.
Tasks: 0 successful, 0 total
Cached: 0 cached, 0 total
Time: 592ms
```
