Wifi-HAL: Avoid possible memleak in nan_debug_command_config

If framework passes a non-positive value for debug_msg_length
to wifihal, it returns without deleting the object created.
This is a memleak. Validate the value of debug_msg_length
before creating object to avoid this memleak.

CRs-Fixed: 2112540
Bug: 72683986
Change-Id: I0c62c219440066b712c899a99be722506f985232
(cherry-picked from e3536a6c2e22fcac948e83ee57a45e81da406c5c)