Malformed error messages from db.mysql real_query fail encoding to json

[einar-hjortdal]

Describe the bug

Error messages are malformed, causing json.encode quiet failures

struct CustomError {
	message   string
	code      int
	data      string
	timestamp string
}

pub fn (e CustomError) code() int {
	return e.code
}

pub fn (e CustomError) msg() string {
	return e.message
}

const error_codes = {
	500: 'Internal Server Error'
}

fn new_custom_error(code int, data string) CustomError {
	return CustomError{
		message: utils.error_codes[code]
		code: code
		data: data
		timestamp: time.now().format_rfc3339()
	}
}

// in an `or` block when `db.mysql` `real_query` returns an error
new_custom_error(500, err.msg())

println(err.msg())
println(new_custom_error)
println(json.encode(new_custom_error))

Outputs

ncorrect string value: 'undefined' for function uuid_to_bin; code: 1411
CustomError{
    message: 'Internal Server Error'
    code: 500
    data: 'ncorrect string value: 'undefined' for function uuid_to_bin; code: 1411'
    timestamp: '2023-11-10T21:26:39.884Z'
}
{"message":"Internal Server Error","code":500,"data":"","timestamp":"2023-11-10T21:26:39.884Z"}

Reproduction Steps

You would have to run the code above and receive error messages from db.mysql real_query.

Because of the nature of this bug, setting up mysql is needed for rull repro

Expected Behavior

json.encode encodes the error string correctly

Current Behavior

json.encode replaces error string with empty string

Possible Solution

db.mysql errors should escape characters correctly.
json.encode should throw a warning or something at runtime when a string is encoded to an empty string

Additional Information/Context

No response

V version

Current V version: V 0.4.2 e7cad4f, timestamp: 2023-11-11 01:10:34 +0300

Environment details (OS name and version, etc.)

V full version: V 0.4.2 95509cf.e7cad4f
OS: linux, Linux version 5.14.0-284.30.1.el9_2.x86_64 (mockbuild@mj.euro.kojibuilder106) (gcc (GCC) 11.3.1 20221121 (Red Hat 11.3.1-4), GNU ld version 2.35.2-37.el9) #1 SMP PREEMPT_DYNAMIC Fri Sep 15 08:06:33 UTC 2023
Processor: 8 cpus, 64bit, little endian, Intel(R) Core(TM) i7-4790K CPU @ 4.00GHz

getwd: /home/coachonko/Documents/projects/vlang/peony
vexe: /home/coachonko/.local/lib64/v/v
vexe mtime: 2023-11-11 07:03:30

vroot: OK, value: /home/coachonko/.local/lib64/v
VMODULES: OK, value: /home/coachonko/.vmodules
VTMP: OK, value: /tmp/v_1000

Git version: git version 2.39.3
Git vroot status: weekly.2023.44-99-ge7cad4f5
.git/config present: true

CC version: cc (GCC) 11.3.1 20221121 (Red Hat 11.3.1-4)
thirdparty/tcc status: thirdparty-linux-amd64 12f392c3

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