feat(db): Improve BuildCaseInsensitiveLike with lowercase (#36598)

Improve BuildCaseInsensitiveLike with lowercase, users are more likely
to input lowercase letters, so lowercase letters are used.

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Signed-off-by: Tyrone Yeh <siryeh@gmail.com>
Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

models/repo/user_repo.go

@@ -151,7 +151,7 @@ func GetRepoAssignees(ctx context.Context, repo *Repository) (_ []*user_model.Us
 func GetIssuePostersWithSearch(ctx context.Context, repo *Repository, isPull bool, search string, isShowFullName bool) ([]*user_model.User, error) {
 	users := make([]*user_model.User, 0, 30)
 	var prefixCond builder.Cond = builder.Like{"lower_name", strings.ToLower(search) + "%"}
-	if isShowFullName {
+	if search != "" && isShowFullName {
 		prefixCond = prefixCond.Or(db.BuildCaseInsensitiveLike("full_name", "%"+search+"%"))
 	}