`-loglevel` ignored in version 0.12.0-alpha.2

**Describe the bug**
Supplying the `-loglevel` flag to ffmpeg seems to make no difference in the output.

**To Reproduce**
Steps to reproduce the behavior:
1. Create `ffmpeg` and wire up logging:

```ts
const ffmpeg = new FFmpeg();
ffmpeg.on(FFmpeg.LOG, ({ message }) => { console.log(message); });
await ffmpeg.load({ /* settings here. */ });
```

2. Run a command, specifying `-loglevel`:

```ts
ffmpeg.exec([
"-f",
"lavfi",
"-i",
"testsrc=​duration=​10:​size=​400x300:​rate=​12",
"-hide_banner",
"-loglevel",
"level+warning",
"testsrc.gif"
]);
```

**Expected behavior**
In this case, warning-level and above output in the console, with level prefixes. See https://ffmpeg.org/ffmpeg.html#Generic-options

**Actual behavior**
No level prefixes, and output significantly more verbose than the desired 'warning' level.

**Desktop (please complete the following information):**
- OS: Mac OSX
- Browser: Chrome
- Version: 108

**Additional context**
Running `ffmpeg-core.js` and `ffmpeg-core.wasm` from version `0.12.0-alpha.2`, downloaded from unpkg, but hosted locally.