add lock for DialogOptional

Author: Yrp

src/main/java/org/tron/common/utils/DialogOptional.java

@@ -14,7 +14,9 @@ private DialogOptional() {
   }
 
   public synchronized DialogOptional setValue(Dialog value) {
-    this.value = Optional.ofNullable(value);
+    if (!this.value.isPresent()) {
+      this.value = Optional.of(value);
+    }
     return this;
   }