fix: skip empty header values in bindData to avoid panic

[skyfireitdiy]

What this PR does

Fixes #3169: BindHeaders panics with index out of range [0] with length 0 when a header value is a nil or empty []string.

The binder now skips entries with no values in both binding paths:

• map path (map[string]string / map[string]any): skip v when len(v) == 0 before indexing v[0]
• struct path: skip inputValue when len(inputValue) == 0 before indexing inputValue[0]

This follows the suggestion from the issue ("skipping entries with no values"). The semantics of []string{""} (a single empty string) are unchanged — only truly empty/nil slices are skipped.

Changes

• bind.go: two len() == 0 guards in bindData
• bind_test.go: new regression test TestBindHeadersEmptyValues covering nil and empty []string against map[string]string, map[string]any, and struct targets

Verification

• go test ./... — all packages pass
• gofmt clean, go vet clean
• Confirmed the new test fails with the exact panic from the issue on the pre-fix code (reproduced via git stash), and passes with the fix