Enable govet nilness check and fix infractions (#2729)

Seems like a reasonable check; removes some unnecessary extra code.

Some of these codepaths don't exist in `bufmod`, but happy to port over
this check and fixes there as well.

.golangci.yml

@@ -19,6 +19,9 @@ linters-settings:
  - '^log\.'
  - '^print$'
  - '^println$'
+ govet:
+ enable:
+ - nilness
  importas:
  alias:
  - pkg: github.com/bufbuild/buf/private/gen/proto/go/buf/alpha/image/v1

private/buf/bufsync/syncer.go

@@ -641,9 +641,6 @@ func (s *syncer) protectSyncedModuleBranch(
  if err != nil {
  return fmt.Errorf("resolve sync point for module %s: %w", moduleIdentity.IdentityString(), err)
  }
- if err != nil {
- return err
- }
  if syncPoint == nil {
  // Branch has never been synced, there is nothing to protected against.
  return nil

private/buf/cmd/buf/command/beta/graph/graph.go

@@ -129,9 +129,6 @@ func run(
  bufcli.NewFetchReader(container.Logger(), storageosProvider, runner, moduleResolver, moduleReader),
  bufmodulebuild.NewModuleBucketBuilder(),
  )
- if err != nil {
- return err
- }
  graphBuilder := bufgraph.NewBuilder(
  container.Logger(),
  moduleResolver,

private/bufpkg/bufimage/bufimagemodify/java_multiple_files.go

@@ -87,7 +87,7 @@ func javaMultipleFilesForFile(
  // The option is already set to the same value, don't do anything.
  return nil
  }
- case options == nil && descriptorpb.Default_FileOptions_JavaMultipleFiles == value:
+ case descriptorpb.Default_FileOptions_JavaMultipleFiles == value:
  // The option is not set, but the value we want to set is the
  // same as the default, don't do anything.
  return nil

private/pkg/protosource/file.go

@@ -638,9 +638,6 @@ func (f *file) populateMessage(
  getMessageExtensionPackedPath(fieldIndex, topLevelMessageIndex, nestedMessageIndexes...),
  getMessageExtensionExtendeePath(fieldIndex, topLevelMessageIndex, nestedMessageIndexes...),
  )
- if err != nil {
- return nil, err
- }
  message.addExtension(field)
  if oneof != nil {
  oneof.addField(field)