Fix index field description parsing

[oleggator]

The schema parsing logic relies on the fact that index field description is always an array. But it may also be a map. This PR fixes that.

Example:

box.cfg { listen = 3301 }
box.schema.user.grant('guest', 'super', nil, nil, { if_not_exists = true })

local space = box.schema.create_space('some_space', { if_not_exists = true })
local index = space:create_index('primary', {
    if_not_exists = true,
    parts = {
        { field = 1, type = 'string', is_nullable = false },
    },
})

local format = box.space[289]:select { space.id, index.id }
print(require('yaml').encode(format))

package main

import (
    "github.com/viciious/go-tarantool"
    "log"
)

func main() {
    _, err := tarantool.Connect("guest@localhost:3301", &tarantool.Options{})
    if err != nil {
        log.Fatalln(err)
    }
}

This code will cause such error:

panic: interface conversion: interface {} is map[string]interface {}, not []interface {}

goroutine 1 [running]:
github.com/viciious/go-tarantool.(*Connection).pullSchema(0xc000120000)
        /Users/o.utkin/go/pkg/mod/github.com/viciious/go-tarantool@v0.0.0-20220525112527-ba97bae22168/connection.go:382 +0x50e
github.com/viciious/go-tarantool.connect({0x121fcd8?, 0xc0000c8008?}, {0xc0000dc120?, 0x0?}, {0xc0000dc12c?, 0x5?}, {0x3b9aca00, 0x3b9aca00, {0x0, 0x0}, ...})
        /Users/o.utkin/go/pkg/mod/github.com/viciious/go-tarantool@v0.0.0-20220525112527-ba97bae22168/connection.go:100 +0xe5
github.com/viciious/go-tarantool.ConnectContext({0x121fcd8, 0xc0000c8008}, {0x11ca4b5?, 0x10403f1?}, 0xc0ffffffff?)
        /Users/o.utkin/go/pkg/mod/github.com/viciious/go-tarantool@v0.0.0-20220525112527-ba97bae22168/connection.go:82 +0x20e
github.com/viciious/go-tarantool.Connect(...)
        /Users/o.utkin/go/pkg/mod/github.com/viciious/go-tarantool@v0.0.0-20220525112527-ba97bae22168/connection.go:87
main.main()
        /xxx/cmd/replicationinfo/main.go:9 +0x77

[viciious]

Thanks a lot! Do you mind adding a test case for this?

[oleggator]

Thanks a lot! Do you mind adding a test case for this?

Done.

[viciious]

Thanks!