fix some code smell problems

1. use Collections.isEmpt() instead of size() > 0
2. make if statements more readable

dolphinscheduler-api/src/main/java/org/apache/dolphinscheduler/api/service/ExecutorService.java

@@ -635,7 +635,7 @@ public class ExecutorService extends BaseService{
      */
     private boolean checkValidForcedSuccessTask(int processInstanceId) {
         List<Integer> forcedSuccessList = processService.findTaskIdByInstanceState(processInstanceId, ExecutionStatus.FORCED_SUCCESS);
-        if (forcedSuccessList != null && forcedSuccessList.size() > 0) {
+        if (forcedSuccessList != null && !forcedSuccessList.isEmpty()) {
             return true;
         }
 

dolphinscheduler-server/src/main/java/org/apache/dolphinscheduler/server/master/runner/MasterExecThread.java

@@ -1186,8 +1186,7 @@ public class MasterExecThread implements Runnable {
             // stop tasks which is retrying if forced success happens
             if (task.taskCanRetry()) {
                 TaskInstance tmpTask = processService.findTaskInstanceById(task.getId());
-                if (tmpTask != null) {
-                    if (tmpTask.getState().equals(ExecutionStatus.FORCED_SUCCESS)) {
+                if (tmpTask != null && tmpTask.getState().equals(ExecutionStatus.FORCED_SUCCESS)) {
                     task.setState(tmpTask.getState());
                     logger.info("task: {} has been forced success, put it into complete task list and stop retrying", task.getName());
                     removeTaskFromStandbyList(task);
@@ -1196,7 +1195,6 @@ public class MasterExecThread implements Runnable {
                     continue;
                 }
             }
-            }
             DependResult dependResult = getDependResultForTask(task);
             if (DependResult.SUCCESS == dependResult) {
                 if (retryTaskIntervalOverTime(task)) {

dolphinscheduler-service/src/main/java/org/apache/dolphinscheduler/service/process/ProcessService.java

@@ -790,7 +790,7 @@ public class ProcessService {
         List<Integer> forcedSuccessList = this.findTaskIdInSubProcessByStatusAndType(taskInstanceId,
                 new ExecutionStatus[]{ExecutionStatus.FORCED_SUCCESS},
                 null);
-        if (forcedSuccessList != null && forcedSuccessList.size() > 0) {
+        if (forcedSuccessList != null && !forcedSuccessList.isEmpty()) {
             return true;
         }