chore: form binding trim space (#38978)

Use "binding:TrimSpace" instead of fragile IsEmptyString

And fix a bug in locale's `HasKey`: it should also try the default
language if current language doesn't have the translation key, a new
test is added.

modules/util/util.go

@@ -13,7 +13,6 @@ import (
 	rand2 "math/rand/v2"
 	"slices"
 	"strconv"
-	"strings"
 	"sync"
 
 	"gitea.dev/modules/container"
@@ -22,11 +21,6 @@ import (
 	"golang.org/x/text/language"
 )
 
-// IsEmptyString checks if the provided string is empty
-func IsEmptyString(s string) bool {
-	return len(strings.TrimSpace(s)) == 0
-}
-
 // ParseYamlBool parses YAML 1.2 boolean values into bool
 func ParseYamlBool(s string) bool {
 	return s == "true" || s == "True" || s == "TRUE"