[codegen/go] Update Go SDK function output to check for errors

Fixes pulumi/pulumi-aws#1872.

This should result in the following sample output in the Go SDK:

```
func GetPolicyDocumentOutput(ctx *pulumi.Context, args GetPolicyDocumentOutputArgs, opts ...pulumi.InvokeOption) GetPolicyDocumentResultOutput {
	return pulumi.ToOutputWithContext(context.Background(), args).
		ApplyT(func(v interface{}) (GetPolicyDocumentResult, error) {
			args := v.(GetPolicyDocumentArgs)
			r, err := GetPolicyDocument(ctx, &args, opts...)
			if err != nil {
				return nil, err
			}
			if r == nil {
				return nil, fmt.Errorf("expected either result or error to be nil, not both")
			}
			return *r, err
		}).(GetPolicyDocumentResultOutput)
}
```

CHANGELOG_PENDING.md

@@ -45,3 +45,6 @@
 
 - [cli] - Stack names correctly take `org set-default` into account when printing.
   [#9240](https://github.com/pulumi/pulumi/pull/9240)
+
+- [codegen/go] - Fix Go SDK function output to check for errors
+  [pulumi-aws#1872](https://github.com/pulumi/pulumi-aws/issues/1872)

pkg/codegen/go/gen.go

@@ -2073,11 +2073,18 @@ func ${fn}Output(ctx *pulumi.Context, args ${fn}OutputArgs, opts ...pulumi.Invok
 		ApplyT(func(v interface{}) (${fn}Result, error) {
 			args := v.(${fn}Args)
 			r, err := ${fn}(ctx, &args, opts...)
+			if err != nil {
+				return nil, err
+			}
+			if r == nil {
+				return nil, fmt.Errorf("expected either result or error to be nil, not both")
+			}
 			return *r, err
 		}).(${outputType})
 }
 
 `
+
 	code = strings.ReplaceAll(code, "${fn}", originalName)
 	code = strings.ReplaceAll(code, "${outputType}", resultTypeName)
 	fmt.Fprintf(w, code)