Even though it is normal, dataman worker thread can not be created

[jeonghwan-lee]

Bug Report

The px4_task_spawn_cmd function passes a value greater than or equal to 0 in the normal case and a value of -1 if an error occurs.
When the dataman start function in dataman.cpp file is running, call the px4_task_spawn_cmd function.
Therefore, in the source code below, the comparison statement that determines the error should be modified to a value less than zero.

// Now
if ((task = px4_task_spawn_cmd("dataman", SCHED_DEFAULT, SCHED_PRIORITY_DEFAULT - 10, 1200, task_main, nullptr)) <= 0) {

// Modified
if ((task = px4_task_spawn_cmd("dataman", SCHED_DEFAULT, SCHED_PRIORITY_DEFAULT - 10, 1200, task_main, nullptr)) < 0) {

[bkueng]

Thanks for the report. Fixed in #7909