fix: reject empty ports in tcp4 address validation

[sergioperezcheco]

Reject an empty TCP4 port

tcp4_addr accepts 127.0.0.1: because net.ResolveTCPAddr treats an empty port as zero. Check the host/port split before resolution and reject an empty port, as discussed in #1003. Explicit :0 remains valid, and the existing IPv4 and port-range checks are preserved.

The regression exercises both Validate.Var and Validate.Struct for empty, missing, zero, normal, maximum, overflowing and negative ports, plus an invalid IPv4 address. The original implementation fails the two empty-port cases; the change passes all nine cases. Native Go 1.26.4 validation passed go test -race -cover ./..., go vet ./..., and golangci-lint v2.13.1 with zero issues. Other OS/Go-version matrix jobs have not been run locally.

Fixes #1003.

• Tests exist or have been written that cover this particular change.

AI-assisted contribution: investigation, implementation, tests and this description were produced with OpenAI GPT-6.1-Sol through Hermes; the commit includes the required model attribution.

[nodivbyzero]

According to the documentation, tcp_addr validates a TCP address.

validator/doc.go

Lines 1302 to 1306 in f3194ca

	# Transmission Control Protocol Address TCP
	This validates that a string value contains a valid resolvable TCP Address.
	Usage: tcp_addr

What is the TCP (or TCP4) address?

IPv4 address: a 32-bit identifier for a network interface, written as four octets (e.g., 192.168.1.10). 

This is what the "address" refers to.

Address does not include port. Am I wrong?