MFC 322270: Fix a NULL pointer dereference in mly_user_command().

If mly_user_command fails to allocate a command slot it jumps to an 'out'
label used for error handling. The error handling code checks for a data
buffer in 'mc->mc_data' to free before checking if 'mc' is NULL. Fix by
just returning directly if we fail to allocate a command and only using
the 'out' label for subsequent errors when there is actual cleanup to
perform.

PR: 217747
Reported by: PVS-Studio