Fix segfault in the CALL macro when no backends are found
Fix segfault in the CALL macro when no backends are found

arrayfire/arrayfire,arrayfire/arrayfire,arrayfire/arrayfire,umar456/arrayfire,arrayfire/arrayfire,9prady9/arrayfire,9prady9/arrayfire,9prady9/arrayfire,umar456/arrayfire,9prady9/arrayfire,umar456/arrayfire,umar456/arrayfire