fix(cli): prevent ariadne from panicking on empty stdin

[daschinmoy21]

Fixes #78

When statix receives an empty string via stdin, an empty Report is generated. Passing an empty string to ariadne's Source::from causes an index out of bounds panic. Supplying a string with a single space as a fallback prevents this panic while keeping the error location at byte offset 0.

Output after this fix-

 echo "" | nix run . -- check -s

[E00] Error: Syntax error
   ╭─[<stdin>:1:1]
   │
 1 │
   · │
   · ╰─ Unexpected end of file
───╯

[mightyiam]

You may be interested in submitting this in https://github.com/molybdenumsoftware/statix, if it is not accepted here.

[daschinmoy21]

Ok . Will open a PR for this change there.Thanks.