Fix for a little parsing issue I took note of
[here](https://github.com/ghostty-org/ghostty/issues/2125#issuecomment-2466537683).
The disparity in behavior between `ghostty@main` and `xterm` can be seen
with this reproduction script:
```sh
printf "\e[0m\nForeground:\n";
printf "\e[38:2:0:255:0mGreen\n";
printf "\e[38;2;0;255;0mGreen\n";
printf "\e[38:2:0:255:0:255mMagenta\n";
printf "\e[38;2;0;255;0;255mGreen\n";
printf "\e[0m\nBackground:\n";
printf "\e[48:2:0:255:0mGreen\n";
printf "\e[48;2;0;255;0mGreen\n";
printf "\e[48:2:0:255:0:255mMagenta\n";
printf "\e[48;2;0;255;0;255mGreen\n";
printf "\e[0m\nUnderline:\n";
printf "\e[58:2:0:255:0m\e[4mGreen\n";
printf "\e[58;2;0;255;0m\e[4mGreen\n";
printf "\e[58:2:0:255:0:255m\e[4mMagenta\n";
printf "\e[58;2;0;255;0;255m\e[4mGreen\n";
printf "\e[0m\n";
```
### Outputs:
|`xterm`|`ghostty@main`|this PR|
|-|-|-|
|<img width="85" alt="image"
src="https://github.com/user-attachments/assets/a0aacff2-2103-4fff-9160-5e663d8a70a2"
/>|<img width="110" alt="image"
src="https://github.com/user-attachments/assets/0ad12e67-3f2c-46f3-b0ee-9230032d188a"
/>|<img width="110" alt="image"
src="https://github.com/user-attachments/assets/7477e3cf-7d27-419e-986b-8df581e52398"
/>|