Don't go for snapshot deletion in case of empty backup (#3250)

<!-- PR description-->

Fix: https://github.com/alcionai/corso/issues/3050 
In case of a blank backup, don't go for snapshot deletion. 

#### Does this PR need a docs update or release note?
- [ ] ⛔ No

#### Type of change

<!--- Please check the type of change your PR introduces: --->
- [x] 🐛 Bugfix

#### Issue(s)

<!-- Can reference multiple issues. Use one of the following "magic words" - "closes, fixes" to auto-close the Github issue. -->
* https://github.com/alcionai/corso/issues/3050

#### Test Plan

<!-- How will this be tested prior to merging.-->
- [x] 💪 Manual
- [ ] ⚡ Unit test

src/pkg/repository/repository.go

@@ -549,10 +549,6 @@ func deleteBackup(
 		return errWrapper(err)
 	}
 
-	if err := kw.DeleteSnapshot(ctx, b.SnapshotID); err != nil {
-		return err
-	}
-
 	if len(b.SnapshotID) > 0 {
 		if err := kw.DeleteSnapshot(ctx, b.SnapshotID); err != nil {
 			return err

src/pkg/repository/repository_unexported_test.go

@@ -112,6 +112,10 @@ func (suite *RepositoryBackupsUnitSuite) TestDeleteBackup() {
 		},
 	}
 
+	bupNoSnapshot := &backup.Backup{
+		BaseModel: model.BaseModel{},
+	}
+
 	table := []struct {
 		name      string
 		sw        mock.BackupWrapper
@@ -172,6 +176,19 @@ func (suite *RepositoryBackupsUnitSuite) TestDeleteBackup() {
 			},
 			expectID: bup.ID,
 		},
+		{
+			name: "no snapshot present",
+			sw: mock.BackupWrapper{
+				Backup:    bupNoSnapshot,
+				GetErr:    nil,
+				DeleteErr: nil,
+			},
+			kw: mockSSDeleter{assert.AnError},
+			expectErr: func(t *testing.T, result error) {
+				assert.NoError(t, result, clues.ToCore(result))
+			},
+			expectID: bupNoSnapshot.ID,
+		},
 	}
 	for _, test := range table {
 		suite.Run(test.name, func() {
@@ -180,7 +197,7 @@ func (suite *RepositoryBackupsUnitSuite) TestDeleteBackup() {
 
 			t := suite.T()
 
-			err := deleteBackup(ctx, string(bup.ID), test.kw, test.sw)
+			err := deleteBackup(ctx, string(test.sw.Backup.ID), test.kw, test.sw)
 			test.expectErr(t, err)
 		})
 	}

src/pkg/store/mock/wrapper.go

@@ -20,6 +20,8 @@ func (bw BackupWrapper) GetBackup(
 	ctx context.Context,
 	backupID model.StableID,
 ) (*backup.Backup, error) {
+	bw.Backup.SnapshotID = bw.Backup.ID.String()
+
 	return bw.Backup, bw.GetErr
 }