sdlog2: fix Segfault on Eagle (#4638)
sdlog2: fix Segfault on Eagle (#4638)

Since orb_exist doesn't work on the Snapdragon Linux side, we need to do
an additional orb_check after the orb_subscribe_multi, otherwise we copy
garbage.

The segfault was triggered by a count/length information about ESC
packets which lead to access outside the struct in the garbage case.
acfloria/Firmware,jlecoeur/Firmware,mcgill-robotics/Firmware,darknight-007/Firmware,acfloria/Firmware,Aerotenna/Firmware,Aerotenna/Firmware,acfloria/Firmware,mcgill-robotics/Firmware,mje-nz/PX4-Firmware,krbeverx/Firmware,dagar/Firmware,mje-nz/PX4-Firmware,jlecoeur/Firmware,dagar/Firmware,krbeverx/Firmware,darknight-007/Firmware,mcgill-robotics/Firmware,mje-nz/PX4-Firmware,PX4/Firmware,darknight-007/Firmware,mcgill-robotics/Firmware,PX4/Firmware,mcgill-robotics/Firmware,acfloria/Firmware,jlecoeur/Firmware,mje-nz/PX4-Firmware,krbeverx/Firmware,Aerotenna/Firmware,krbeverx/Firmware,mje-nz/PX4-Firmware,PX4/Firmware,dagar/Firmware,mcgill-robotics/Firmware,jlecoeur/Firmware,dagar/Firmware,jlecoeur/Firmware,darknight-007/Firmware,mje-nz/PX4-Firmware,dagar/Firmware,jlecoeur/Firmware,Aerotenna/Firmware,dagar/Firmware,PX4/Firmware,Aerotenna/Firmware,Aerotenna/Firmware,krbeverx/Firmware,jlecoeur/Firmware,krbeverx/Firmware,acfloria/Firmware,krbeverx/Firmware,jlecoeur/Firmware,PX4/Firmware,dagar/Firmware,acfloria/Firmware,mcgill-robotics/Firmware,PX4/Firmware,acfloria/Firmware,darknight-007/Firmware,mje-nz/PX4-Firmware,Aerotenna/Firmware,PX4/Firmware