fix: fix redownload when the remote repo has no mod file

[zong-zhe]

1. Does this PR affect any open issues?(Y/N) and add issue references (e.g. "fix #123", "re #123".):

• N
• Y

2. What is the scope of this PR (e.g. component or file name):

3. Provide a description of the PR(e.g. more details, effects, motivations or doc link):

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Other

4. Are there any breaking changes?(Y/N) and describe the breaking changes(e.g. more details, motivations or doc link):

• N
• Y

5. Are there test cases for these changes?(Y/N) select and add more details, references or doc links:

• Unit test
• Integration test
• Benchmark (add benchmark stats below)
• Manual test (add detailed scripts or steps below)
• Other

[Peefy]

LGTM

[coveralls]

Pull Request Test Coverage Report for Build 11812766281

Details

• 31 of 41 (75.61%) changed or added relevant lines in 3 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.3%) to 42.494%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
pkg/downloader/downloader.go	0	1	0.0%
pkg/package/modfile.go	0	1	0.0%
pkg/client/test.go	31	39	79.49%

Totals
Change from base Build 11797598770:	0.3%
Covered Lines:	4014
Relevant Lines:	9446

---

💛 - Coveralls