Remove redundant len check around loop (#27464)

This pull request is a minor code cleanup.

From the Go specification (https://go.dev/ref/spec#For_range):

> "1. For a nil slice, the number of iterations is 0."
> "3. If the map is nil, the number of iterations is 0."

`len` returns 0 if the slice or map is nil
(https://pkg.go.dev/builtin#len). Therefore, checking `len(v) > 0`
before a loop is unnecessary.

---

At the time of writing this pull request, there wasn't a lint rule that
catches these issues. The closest I could find is
https://staticcheck.dev/docs/checks/#S103

Signed-off-by: Eng Zer Jun <engzerjun@gmail.com>

routers/web/repo/issue.go

@@ -965,10 +965,8 @@ func NewIssue(ctx *context.Context) {
 
 	_, templateErrs := issue_service.GetTemplatesFromDefaultBranch(ctx.Repo.Repository, ctx.Repo.GitRepo)
 	templateLoaded, errs := setTemplateIfExists(ctx, issueTemplateKey, IssueTemplateCandidates)
-	if len(errs) > 0 {
-		for k, v := range errs {
-			templateErrs[k] = v
-		}
+	for k, v := range errs {
+		templateErrs[k] = v
 	}
 	if ctx.Written() {
 		return