RDS: Add a warning if trying to allocate 0 sgs
RDS: Add a warning if trying to allocate 0 sgs

rds_message_alloc_sgs() only works when nents is nonzero.

Signed-off-by: Andy Grover <f97dd4ff5f39846680e670bd8c5a456390ee8b8b@oracle.com>

TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas