Fix #269: Correct error checking for taskSpawn

The test for failure of taskSpawn should be for the value of
ERROR, not 0, per the VxWorks API documentation.

Found when implementing the unit test improvements in #230.
This issue is generally only reproducible in UT where taskSpawn
can be made to fail.

src/os/vxworks/osapi.c

@@ -1759,7 +1759,7 @@ int32 OS_ConsoleCreate_Impl(uint32 local_id)
                     (FUNCPTR)OS_ConsoleTask_Entry,
                     local_id,0,0,0,0,0,0,0,0,0);
 
-            if (local->taskid == (TASK_ID)0)
+            if (local->taskid == (TASK_ID)ERROR)
             {
                 OS_DEBUG("taskSpawn() - vxWorks errno %d\n",errno);
                 return_code = OS_ERROR;