mlibc printf panic

The following print format string causes a mlibc panic: `%1$.*2$f%3$s`. This was found in GNU Parted and presumably works on other libcs.

Logs:

```
vsnprintf(%1$.*2$f%3$s)
mlibc: Unknown printf terminator '50'
In function operator(), file ../../../base_dir/sources/mlibc/options/ansi/generic/stdio.cpp:82
__ensure(!"Illegal printf terminator") failed
```