skip migration on new db

[gertd]

Skip migration when the target database file does not exist, preventing the creation of the migration version backups.

[github-actions]

Pull Request Test Coverage Report for Build 6900099376

• 78 of 111 (70.27%) changed or added relevant lines in 7 files are covered.
• 319 unchanged lines in 9 files lost coverage.
• Overall coverage decreased (-8.1%) to 28.985%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
pkg/bdb/boltdb.go	1	3	33.33%
pkg/bdb/metadata.go	1	3	33.33%
pkg/bdb/migrate/mig/mig.go	3	5	60.0%
pkg/fs/fs.go	14	17	82.35%
pkg/bdb/migrate/mig003/migrate.go	39	51	76.47%
pkg/bdb/migrate/migrate.go	14	26	53.85%

Files with Coverage Reduction	New Missed Lines	%
pkg/directory/directory.go	4	75.0%
pkg/bdb/boltdb.go	7	54.17%
pkg/bdb/metadata.go	7	66.04%
pkg/bdb/generic.go	12	53.52%
pkg/bdb/migrate/mig001/migrate.go	25	0.0%
pkg/bdb/migrate/mig002/migrate.go	54	4.05%
pkg/bdb/migrate/mig/mig.go	56	35.85%
pkg/bdb/migrate/migrate.go	64	13.77%
pkg/bdb/migrate/mig003/migrate.go	90	20.24%

Totals
Change from base Build 6869955631:	-8.1%
Covered Lines:	1002
Relevant Lines:	3457

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💛 - Coveralls