Panic in checkForErrors when the service responds with an Internal Service Error

[emaildanwilson]

The client hits the error:

panic: interface conversion: interface {} is nil, not []interface {}

Maybe it can bail if the error is >= 500?

2021/02/23 21:42:07 client.go:224: In GET by ID : &{GET https://api.dns.constellix.com/v1/domains/REDACTED/records/cname/search?exact=observer-workload-REDACTED HTTP/1.1 1 1 map[Content-Type:[application/json] X-Cns-Security-Token:[REDACTED]] <nil> <nil> 0 [] false api.dns.constellix.com map[] map[] <nil> map[]   <nil> <nil> <nil> 0xc0000b8020}
2021/02/23 21:42:07 client.go:231: Response for Get:  &{500 Internal Server Error 500 HTTP/1.1 1 1 map[Cnsdns-Account-Id:[REDACTED] Cnsdns-User-Role:[] Connection:[keep-alive] Content-Language:[en] Content-Type:[text/html;charset=utf-8] Date:[Tue, 23 Feb 2021 21:42:07 GMT] Requestlimitheader:[70] Requestlimitinterval:[10.00] Requestlimitrate:[7.00] Requestrefreshinterval:[0] Requestsremainingheader:[0] Server:[Apache-Coyote/1.1]] 0xc000cd1140 -1 [chunked] false false map[] 0xc000b60f00 0xc000a2b8c0}
panic: interface conversion: interface {} is nil, not []interface {}

goroutine 6838 [running]:
github.com/Constellix/constellix-go-client/client.checkForErrors(0xc00160b710, 0x2, 0x2)
	~/go/pkg/mod/github.com/!constellix/constellix-go-client@v1.0.1/client/client.go:184 +0x43f
github.com/Constellix/constellix-go-client/client.(*Client).GetbyId(0xc000639340, 0xc00101db30, 0x4c, 0x6, 0xc00101db30, 0x4c)
	~/go/pkg/mod/github.com/!constellix/constellix-go-client@v1.0.1/client/client.go:233 +0x26b