android: bind v4 server to real interface IP instead of 0.0.0.0

tools/chatgui-android/app/src/main/java/com/utun/chat/data/ConfigProvider.kt

@@ -307,7 +307,7 @@ class ConfigProvider(private val context: Context) {
             for (srv in servers) {
                 val family = if (srv.bindIp.contains(":")) "v6" else "v4"
                 appendLine("[server:${srv.ifName}_$family]")
-                appendLine("addr=${if (family == "v6") "[::]" else "0.0.0.0"}:${srv.port}")
+                appendLine("addr=${if (family == "v6") "[::]" else srv.bindIp.ifBlank { "0.0.0.0" }}:${srv.port}")
                 appendLine("type=public")
                 appendLine("transport=${srv.protocol}")
                 if (family == "v6") appendLine("netif=${srv.ifName}")