Bug Fix, Empty Group

[samatspothero]

When removing the only user from a group, this code was failing because the db connection was returning an empty array "{}" instead of a null. This was causing the cast to integer a few lines down to fail with

panic: strconv.Atoi: parsing "": invalid syntax

This PR changes the code to check for that case and enter the else branch to assign an empty array to the state.

[samatspothero]

@frankfarrell Any thoughts on this?

[schwartzmx]

Also just ran into this issue

Stack trace from the terraform-provider-redshift_v0.0.3 plugin:

panic: strconv.Atoi: parsing "": invalid syntax

goroutine 27 [running]:
github.com/frankfarrell/terraform-provider-redshift/redshift.readRedshiftGroup(0xc00024d810, 0xc000480c00, 0xc000128000, 0x0)
        /build/redshift/resource_redshift_group.go:151 +0x5d7
github.com/frankfarrell/terraform-provider-redshift/redshift.resourceRedshiftGroupRead(0xc00024d810, 0xd1b960, 0xc00024ddc0, 0xc00024d810, 0x0)
        /build/redshift/resource_redshift_group.go:116 +0x9e
github.com/hashicorp/terraform/helper/schema.(*Resource).RefreshWithoutUpgrade(0xc000196a00, 0xc0005cdb80, 0xd1b960, 0xc00024ddc0, 0xc0001f0030, 0xc0005cdb80, 0x0)
        /go/pkg/mod/github.com/hashicorp/terraform@v0.12.2/helper/schema/resource.go:447 +0x12e
github.com/hashicorp/terraform/helper/plugin.(*GRPCProviderServer).ReadResource(0xc00013ca48, 0xfea5d0, 0xc0005ffd40, 0xc0005cda90, 0xc00013ca48, 0xc0005ffd40, 0xc0001d9a50)
        /go/pkg/mod/github.com/hashicorp/terraform@v0.12.2/helper/plugin/grpc_provider.go:499 +0x332
github.com/hashicorp/terraform/internal/tfplugin5._Provider_ReadResource_Handler(0xe561c0, 0xc00013ca48, 0xfea5d0, 0xc0005ffd40, 0xc0005cda40, 0x0, 0xfea5d0, 0xc0005ffd40, 0xc000316230, 0x43)
        /go/pkg/mod/github.com/hashicorp/terraform@v0.12.2/internal/tfplugin5/tfplugin5.pb.go:3181 +0x214
google.golang.org/grpc.(*Server).processUnaryRPC(0xc000304900, 0xff20d8, 0xc000001e00, 0xc0001bf100, 0xc00030e5d0, 0x14bc830, 0x0, 0x0, 0x0)
        /go/pkg/mod/google.golang.org/grpc@v1.18.0/server.go:966 +0x486
google.golang.org/grpc.(*Server).handleStream(0xc000304900, 0xff20d8, 0xc000001e00, 0xc0001bf100, 0x0)
        /go/pkg/mod/google.golang.org/grpc@v1.18.0/server.go:1245 +0xcbd
google.golang.org/grpc.(*Server).serveStreams.func1.1(0xc000038240, 0xc000304900, 0xff20d8, 0xc000001e00, 0xc0001bf100)
        /go/pkg/mod/google.golang.org/grpc@v1.18.0/server.go:685 +0xab
created by google.golang.org/grpc.(*Server).serveStreams.func1
        /go/pkg/mod/google.golang.org/grpc@v1.18.0/server.go:683 +0xa5

Error: The terraform-provider-redshift_v0.0.3 plugin crashed!

was able to work around it by manually re-adding some things back on the redshift side to alleviate the panic.