Fix minor parser errors

[mxork]

I was messing around and found a couple minor bugs in the parser.

1. Failure on reading a numeric like 1.
2. Failure on parsing a return statement without any return values
3. No srcloc reporting if current-source-name is false

Test program:

#lang racket

(require lua/lang/parser
               lua/lang/lexer)

(parse-chunk (make-lexer (open-input-string "return 1.")))
(parse-chunk (make-lexer (open-input-string "return")))

My changes are a little tasteless, but I think they're sound. The digit change is covered by lua:read-number. parse-exprs* parses zero or more expressions via copy-pasta.

[mxork]

I'm not planning on fixing this, but hex numbers with decimal points fail to parse. They do in lua:

Lua 5.4.8  Copyright (C) 1994-2025 Lua.org, PUC-Rio
> 0x.1
0.0625

[Bogdanp]

Thanks!