Memory Safety: Medium
Two calloc() calls in backend-native.c do not check the return value
before dereferencing the pointer:
1. rfcomm_send_cmd_enqueue() allocates an rfcomm_cmd struct and
immediately passes cmd->cmd to vsnprintf without a NULL check.
2. rfcomm_hfp_ag_clcc() allocates an updated_call struct and
immediately dereferences updated_call->id without a NULL check.
Both would crash on allocation failure. Add NULL checks that return
an error instead of dereferencing NULL.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
