MDBF-534: Coverity scan: fix client folder

```------------------------------
File: `mysqlslap`
```

------------------------------
- Coverity (CHECKED_RETURN):
  https://scan5.scan.coverity.com/reports.htm#v58936/p10357/fileInstanceId=231728428&defectInstanceId=53073524&mergedDefectId=1520114

- FALSE POSITIVES
  - Coverity (DC.WEAK_CRYPTO) (`random()`):
    https://scan5.scan.coverity.com/reports.htm#v58936/p10357/fileInstanceId=231728428&defectInstanceId=53073112&mergedDefectId=1225806
    https://scan5.scan.coverity.com/reports.htm#v58936/p10357/fileInstanceId=231728428&defectInstanceId=53074491&mergedDefectId=1409160
    https://scan5.scan.coverity.com/reports.htm#v58936/p10357/fileInstanceId=231728428&defectInstanceId=53074151&mergedDefectId=1409180
    https://scan5.scan.coverity.com/reports.htm#v58936/p10357/fileInstanceId=231728428&defectInstanceId=53073799&mergedDefectId=1409183

  - Coverity (TAINTED_SCALAR):
    https://scan5.scan.coverity.com/reports.htm#v58936/p10357/fileInstanceId=231728428&defectInstanceId=53074667&mergedDefectId=1519586
  - Coverity (UNINT):
  - Coverity (BAD_FREE):
    https://scan5.scan.coverity.com/reports.htm#v58936/p10357/fileInstanceId=231728428&defectInstanceId=53074415&mergedDefectId=1520371

client/mysqlslap.c

@@ -1768,6 +1768,7 @@ run_scheduler(stats *sptr, statement *stmts, uint concur, ulonglong limit)
   uint x;
   struct timeval start_time, end_time;
   thread_context con;
+  int error;
   pthread_t mainthread;            /* Thread descriptor */
   pthread_attr_t attr;          /* Thread attributes */
   DBUG_ENTER("run_scheduler");
@@ -1776,8 +1777,11 @@ run_scheduler(stats *sptr, statement *stmts, uint concur, ulonglong limit)
   con.limit= limit;
 
   pthread_attr_init(&attr);
-  pthread_attr_setdetachstate(&attr,
-		  PTHREAD_CREATE_DETACHED);
+  if ((error= pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED)))
+  {
+    printf("Got error: %d from pthread_attr_setdetachstate\n", error);
+    exit(1);
+  }
 
   pthread_mutex_lock(&counter_mutex);
   thread_counter= 0;