fix panic when get with table output for resource w/o expected output (…

…flyteorg#168)

`flytectl get task/workflow/launchplan -o table` panics if resource has no expected output.
We encountered `FormatVariableDescriptions at pkg/printer/printer.go:173` to panic when using
the get commands on a resource without expected output.
This happened with both explicit table output as well as default.

Replicated on lastest master, workflow demo-1.no-output has no expected output:

```
$ go run ./main.go get launchplans -p demo-1 -d production --latest demo-1.no-output

panic: assignment to entry in nil map

goroutine 1 [running]:
github.com/flyteorg/flytectl/pkg/printer.FormatVariableDescriptions(0x0)
	/workspace/flyteorg/flytectl/pkg/printer/printer.go:202 +0x307
github.com/flyteorg/flytectl/cmd/get.LaunchplanToTableProtoMessages({0xc000a30938, 0x1, 0x7ffeefbff977})
	/workspace/flyteorg/flytectl/cmd/get/launch_plan.go:136 +0xee
github.com/flyteorg/flytectl/cmd/get.getLaunchPlanFunc({0x2dfbf98, 0xc0000580b8}, {0xc0002fb8c0, 0x1, 0x11519b4}, {{0x2e55850, 0xc000a30120}, {0x2e472c0, 0xc0009a3110}, {0x2ddff60, ...}, ...})
	/workspace/flyteorg/flytectl/cmd/get/launch_plan.go:158 +0x307
github.com/flyteorg/flytectl/cmd/core.generateCommandFunc.func1(0xc000481680, {0xc0002fb8c0, 0x1, 0x6})
	/workspace/flyteorg/flytectl/cmd/core/cmd.go:69 +0x47d
github.com/spf13/cobra.(*Command).execute(0xc000481680, {0xc0002fb860, 0x6, 0x6})
	/workspace/go/pkg/mod/github.com/spf13/[email protected]/command.go:852 +0x60e
github.com/spf13/cobra.(*Command).ExecuteC(0xc000480000)
	/workspace/go/pkg/mod/github.com/spf13/[email protected]/command.go:960 +0x3ad
github.com/spf13/cobra.(*Command).Execute(...)
	/workspace/go/pkg/mod/github.com/spf13/[email protected]/command.go:897
github.com/flyteorg/flytectl/cmd.ExecuteCmd()
	/workspace/flyteorg/flytectl/cmd/root.go:135 +0x1e
main.main()
	/workspace/flyteorg/flytectl/main.go:12 +0x1d
exit status 2
```

Simple fix:
nil checks exists for container but not on the map itself prior to calling, and nil input causes the panic.
Added nil check on map parameter prior to calling in all places found.

Signed-off-by: Viktor Gerdin <[email protected]>

flytectl/cmd/get/launch_plan.go

@@ -132,7 +132,7 @@ func LaunchplanToTableProtoMessages(l []*admin.LaunchPlan) []proto.Message {
 			if m.Closure.ExpectedInputs != nil {
 				printer.FormatParameterDescriptions(m.Closure.ExpectedInputs.Parameters)
 			}
-			if m.Closure.ExpectedOutputs != nil {
+			if m.Closure.ExpectedOutputs != nil && m.Closure.ExpectedOutputs.Variables != nil {
 				printer.FormatVariableDescriptions(m.Closure.ExpectedOutputs.Variables)
 			}
 		}

flytectl/cmd/get/task.go

@@ -119,10 +119,10 @@ func TaskToTableProtoMessages(l []*admin.Task) []proto.Message {
 		if m.Closure != nil && m.Closure.CompiledTask != nil {
 			if m.Closure.CompiledTask.Template != nil {
 				if m.Closure.CompiledTask.Template.Interface != nil {
-					if m.Closure.CompiledTask.Template.Interface.Inputs != nil {
+					if m.Closure.CompiledTask.Template.Interface.Inputs != nil && m.Closure.CompiledTask.Template.Interface.Inputs.Variables != nil {
 						printer.FormatVariableDescriptions(m.Closure.CompiledTask.Template.Interface.Inputs.Variables)
 					}
-					if m.Closure.CompiledTask.Template.Interface.Outputs != nil {
+					if m.Closure.CompiledTask.Template.Interface.Outputs != nil && m.Closure.CompiledTask.Template.Interface.Outputs.Variables != nil {
 						printer.FormatVariableDescriptions(m.Closure.CompiledTask.Template.Interface.Outputs.Variables)
 					}
 				}

flytectl/cmd/get/workflow.go

@@ -114,10 +114,10 @@ func WorkflowToTableProtoMessages(l []*admin.Workflow) []proto.Message {
 			if m.Closure.CompiledWorkflow.Primary != nil {
 				if m.Closure.CompiledWorkflow.Primary.Template != nil {
 					if m.Closure.CompiledWorkflow.Primary.Template.Interface != nil {
-						if m.Closure.CompiledWorkflow.Primary.Template.Interface.Inputs != nil {
+						if m.Closure.CompiledWorkflow.Primary.Template.Interface.Inputs != nil && m.Closure.CompiledWorkflow.Primary.Template.Interface.Inputs.Variables != nil {
 							printer.FormatVariableDescriptions(m.Closure.CompiledWorkflow.Primary.Template.Interface.Inputs.Variables)
 						}
-						if m.Closure.CompiledWorkflow.Primary.Template.Interface.Outputs != nil {
+						if m.Closure.CompiledWorkflow.Primary.Template.Interface.Outputs != nil && m.Closure.CompiledWorkflow.Primary.Template.Interface.Outputs.Variables != nil {
 							printer.FormatVariableDescriptions(m.Closure.CompiledWorkflow.Primary.Template.Interface.Outputs.Variables)
 						}
 					}