fix: use default CoAP port as fallback for request URLs

[JKRhb]

This PR fixes the error

RangeError: Port should be > 0 and < 65536. Received .

that occurred when passing a URL to the request node that contained no explicit port number.

[coveralls]

Pull Request Test Coverage Report for Build 2307592500

• 6 of 6 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.6%) to 81.343%

---

Totals
Change from base Build 2258753508:	0.6%
Covered Lines:	151
Relevant Lines:	178

---

💛 - Coveralls

[coveralls]

Pull Request Test Coverage Report for Build 2307574262

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

• For more information on this, see Tracking coverage changes with pull request builds.
• To avoid this issue with future PRs, see these Recommended CI Configurations.
• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 6 of 6 (100.0%) changed or added relevant lines in 1 file are covered.
• 5 unchanged lines in 1 file lost coverage.
• Overall coverage increased (+0.8%) to 81.55%

---

Files with Coverage Reduction	New Missed Lines	%
coap/coap-request.js	5	93.58%

Totals
Change from base Build 2258753508:	0.8%
Covered Lines:	152
Relevant Lines:	179

---

💛 - Coveralls