fix(code):修复报送 extra无数据的问题。

Assets/Plugins/iOS/UnityBridge.mm

@@ -234,8 +234,9 @@ extern "C" {
                 [keyValuePairs addObject:[NSString stringWithFormat:@"%@:%@", key, value]];
             }];
             playerInfo.extra = [keyValuePairs componentsJoinedByString:@";"];
+        }else if ([extraObj isKindOfClass:[NSString class]]) {
+            playerInfo.extra = (NSString *)extraObj;
         }
-        
         [sdk report:(EventType)eventType data:playerInfo];
     }