Do not terminate listing for token-based pagination resources on empt…

…y response (#530)

## Changes
It is allowed for list APIs to return less than the number of resources
in the page_size limit in a response. In case no items are returned but
there are still items to list, we should continue to list resources
until no next_page_token is included in the response. This matches the
logic from the Go SDK:
https://github.com/databricks/databricks-sdk-go/blob/main/.codegen/api.go.tmpl#L275-L294

## Tests
- [x] Nightly tests pass.

.codegen/service.py.tmpl

@@ -270,29 +270,32 @@ class {{.Name}}API:{{if .Description}}
         {{- end}}
         while True:
           json = {{template "method-do" .}}
-          if '{{.Pagination.Results.Name}}' not in json or not json['{{.Pagination.Results.Name}}']:
+          if '{{.Pagination.Results.Name}}' in json:
+            for v in json['{{.Pagination.Results.Name}}']:
+              {{if .NeedsOffsetDedupe -}}
+              i = v['{{.IdentifierField.Name}}']
+              if i in seen:
+                continue
+              seen.add(i)
+              {{end -}}
+              yield {{.Pagination.Entity.PascalName}}.from_dict(v)
+          {{ if .Pagination.Token -}}
+          if '{{.Pagination.Token.Bind.Name}}' not in json or not json['{{.Pagination.Token.Bind.Name}}']:
             return
-          for v in json['{{.Pagination.Results.Name}}']:
-            {{if .NeedsOffsetDedupe -}}
-            i = v['{{.IdentifierField.Name}}']
-            if i in seen:
-              continue
-            seen.add(i)
-            {{end -}}
-            yield {{.Pagination.Entity.PascalName}}.from_dict(v)
-          {{if eq .Path "/api/2.0/clusters/events" -}}
+          {{if eq "GET" .Verb}}query{{else}}body{{end}}['{{.Pagination.Token.PollField.Name}}'] = json['{{.Pagination.Token.Bind.Name}}']
+          {{- else if eq .Path "/api/2.0/clusters/events" -}}
           if 'next_page' not in json or not json['next_page']:
             return
           body = json['next_page']
-          {{- else if .Pagination.Token -}}
-          if '{{.Pagination.Token.Bind.Name}}' not in json or not json['{{.Pagination.Token.Bind.Name}}']:
+          {{- else -}}
+          if '{{.Pagination.Results.Name}}' not in json or not json['{{.Pagination.Results.Name}}']:
             return
-          {{if eq "GET" .Verb}}query{{else}}body{{end}}['{{.Pagination.Token.PollField.Name}}'] = json['{{.Pagination.Token.Bind.Name}}']
-          {{- else if eq .Pagination.Increment 1 -}}
+          {{ if eq .Pagination.Increment 1 -}}
           query['{{.Pagination.Offset.Name}}'] += 1
           {{- else -}}
           query['{{.Pagination.Offset.Name}}'] += len(json['{{.Pagination.Results.Name}}'])
           {{- end}}
+          {{- end}}
         {{else -}}
         json = {{template "method-do" .}}
         parsed = {{.Response.PascalName}}.from_dict(json).{{template "safe-snake-name" .Pagination.Results}}