Two escaped chars in bacticks break the builder.

[katekyy]

Describe the bug

It appears that when you put 2 escaped chars in a pair of bacticks, like you would with a rune, cgen (looking briefly at the stack trace) just breaks.

Reproduction Steps

fn main() {
	dump(`\n\t`)
}

Expected Behavior

main.v:2:7: error: invalid character literal `\n\t` => `\n\t` ([`\n`, `\t`]) (more than one character)
    1 | fn main() {
    2 |     dump(`\n\t`)
      |          ^
    3 | }
Details: 
main.v:2:7: details: use quotes for strings, backticks for characters
    1 | fn main() {
    2 |     dump(`\n\t`)
      |          ^
    3 | }

Current Behavior

V panic: substr(4, 2) out of bounds (len=4)
v hash: 680b0d4
/tmp/v_0/v2.15182888585928238289.tmp.c:21294: at _v_panic: Backtrace
/tmp/v_0/v2.15182888585928238289.tmp.c:24659: by string_substr
/tmp/v_0/v2.15182888585928238289.tmp.c:57682: by v__scanner__Scanner_decode_o_escapes
/tmp/v_0/v2.15182888585928238289.tmp.c:57818: by v__scanner__Scanner_ident_char
/tmp/v_0/v2.15182888585928238289.tmp.c:57033: by v__scanner__Scanner_text_scan
/tmp/v_0/v2.15182888585928238289.tmp.c:56821: by v__scanner__Scanner_scan_remaining_text
/tmp/v_0/v2.15182888585928238289.tmp.c:56809: by v__scanner__Scanner_scan_all_tokens_in_buffer
/tmp/v_0/v2.15182888585928238289.tmp.c:56331: by v__scanner__new_scanner_file
/tmp/v_0/v2.15182888585928238289.tmp.c:18321: by v__parser__parse_file
/tmp/v_0/v2.15182888585928238289.tmp.c:18659: by v__parser__parse_files
/tmp/v_0/v2.15182888585928238289.tmp.c:48933: by v__builder__Builder_front_stages
/tmp/v_0/v2.15182888585928238289.tmp.c:48987: by v__builder__Builder_front_and_middle_stages
/tmp/v_0/v2.15182888585928238289.tmp.c:51442: by v__builder__cbuilder__gen_c
/tmp/v_0/v2.15182888585928238289.tmp.c:51425: by v__builder__cbuilder__build_c
/tmp/v_0/v2.15182888585928238289.tmp.c:51415: by v__builder__cbuilder__compile_c
/tmp/v_0/v2.15182888585928238289.tmp.c:51321: by v__builder__Builder_rebuild
/tmp/v_0/v2.15182888585928238289.tmp.c:50426: by v__builder__compile
/tmp/v_0/v2.15182888585928238289.tmp.c:51756: by main__rebuild
/tmp/v_0/v2.15182888585928238289.tmp.c:51704: by main__main
/tmp/v_0/v2.15182888585928238289.tmp.c:52425: by main
Exited with error status 1
Please try again.

Possible Solution

Since this would still be an error, just don't do that.

Additional Information/Context

No response

V version

V 0.4.3 8f76a06

Environment details (OS name and version, etc.)

V full version: V 0.4.3 8f76a06.680b0d4
OS: linux, Linux version 6.1.68-1-lts (linux-lts@archlinux) (gcc (GCC) 13.2.1 20230801, GNU ld (GNU Binutils) 2.41.0) #1 SMP PREEMPT_DYNAMIC Wed, 13 Dec 2023 18:48:47 +0000
Processor: 8 cpus, 64bit, little endian, 11th Gen Intel(R) Core(TM) i5-1135G7 @ 2.40GHz

vroot: OK, value: /home/katekyy/.local/share/v
VMODULES: OK, value: /home/katekyy/.vmodules
VTMP: OK, value: /tmp/v_1000

Git version: git version 2.43.0
Git vroot status: weekly.2023.52-14-g680b0d46
.git/config present: true

CC version: cc (GCC) 13.2.1 20230801
thirdparty/tcc status: thirdparty-linux-amd64 12f392c3

[katekyy]

Additionally. If you put a normal char after the escaped one, it thinks that there are 3 characters there. Well, technically there are, but that's not how the error message should look like.

                                                                   Here
                                                             vvvvvvvvvvvvvvv
main.v:2:7: error: invalid character literal `\na` => `\na` ([`\`, `n`, `a`]) (more than one character)
    1 | fn main() {
    2 |     dump(`\na`)
      |          ^
    3 | }
Details: 
main.v:2:7: details: use quotes for strings, backticks for characters
    1 | fn main() {
    2 |     dump(`\na`)
      |          ^
    3 | }