Fix out of bounds access when parsing end_pos

[BradLewis]

We got an error reported in ols:

".../ols/ols"  "stderr"        ".../odin/core/odin/parser/parser.odin(103:14) Invalid slice indices 0:2 is out of range 0..<1\n"

My guess is we have a string with the tokenizer text only being 1 character, though I'm not really sure how that happens.

Edit: I changed it to just explicitly verify the length as I'm not even sure how it got into the state of having this error.

[laytan]

I am guessing it happens on this?

foo :: ``

Hmm on second look, I think not

[BradLewis]

That was my guess but it seems fine for me, and that should have length 2 for the two quote characters. I also tried with just

foo :: ` // also ' and "

but that seemed to be fine as well

[laytan]

Probably an unterminated string (at the end of the file?) actually, where you do get a syntax error but we return an incomplete string token.

[BradLewis]

Ah yeah I'm able to reproduce it with the very minimal program now

package main

foo :: "

It just doesn't cause any issues with ols but will crash when manually parsing the file.