manager/csi: add missing nil check in PublishVolume, UnpublishVolume

[thaJeztah]

Both makeControllerPublishVolumeRequest and makeControllerUnpublishVolumeRequest check if the VolumeInfo is nil, in which case they would produce a nil request;

func (p *plugin) makeControllerPublishVolumeRequest(v *api.Volume, nodeID string) *csi.ControllerPublishVolumeRequest {
    if v.VolumeInfo == nil {
        return nil
    }
    ...

func (p *plugin) makeControllerUnpublishVolumeRequest(v *api.Volume, nodeID string) *csi.ControllerUnpublishVolumeRequest {
    if v.VolumeInfo == nil {
        return nil
    }
    ...

This request which would be sent to the CSI controller-client, potentially resulting in an obscure error during marshaling;

rpc error: code = Internal desc = grpc: error while marshaling: proto: Marshal called with nil

Update PublishVolume and UnpublishVolume to return early, similar to the existing check in DeleteVolume;

func (p *plugin) DeleteVolume(ctx context.Context, v *api.Volume) error {
    if v.VolumeInfo == nil {
        return errors.New("VolumeInfo must not be nil")
    }

- What I did

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- Description for the changelog

[codecov-commenter]

Codecov Report

❌ Patch coverage is 55.55556% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 14.73%. Comparing base (6e9e7b8) to head (dbe7dae).
⚠️ Report is 60 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #3277   +/-   ##
=======================================
  Coverage   14.73%   14.73%           
=======================================
  Files         200      200           
  Lines       93077    93025   -52     
=======================================
- Hits        13712    13711    -1     
+ Misses      78019    77968   -51     
  Partials     1346     1346           

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