Fix and improve port hopping interval handling

https://github.com/2dust/v2rayNG/issues/5171

V2rayNG/app/src/main/java/com/v2ray/ang/extension/_Ext.kt

@@ -168,7 +168,7 @@ inline fun <reified T : Serializable> Intent.serializable(key: String): T? = whe
  *
  * @return True if the CharSequence is not null and not empty, false otherwise.
  */
-fun CharSequence?.isNotNullEmpty(): Boolean = this != null && this.isNotEmpty()
+fun CharSequence?.isNotNullEmpty(): Boolean = !this.isNullOrBlank()
 
 fun String.concatUrl(vararg paths: String): String {
     val builder = StringBuilder(this.trimEnd('/'))

V2rayNG/app/src/main/java/com/v2ray/ang/handler/V2rayConfigManager.kt

@@ -1227,7 +1227,11 @@ object V2rayConfigManager {
                 if (profileItem.portHopping.isNotNullEmpty()) {
                     hysteriaSetting.udphop = StreamSettingsBean.HysteriaSettingsBean.HysteriaUdpHopBean(
                         port = profileItem.portHopping,
-                        interval = profileItem.portHoppingInterval?.ifEmpty { "30" }.orEmpty().toInt()
+                        interval = profileItem.portHoppingInterval
+                            ?.trim()
+                            ?.toIntOrNull()
+                            ?.takeIf { it >= 5 }
+                            ?: 30
                     )
                 }
                 streamSettings.hysteriaSettings = hysteriaSetting