diag: dci:Safeguard to prevent Integer Underflow and Memory Leak

At certain point in diag driver there can be integer underflow
thus can lead to memory leak. Added a safeguard for that.

Change-Id: Ic4d97df62d3f65566ffa6d2d7daa35f4485e3f2c
CRs-fixed: 556860
Signed-off-by: Katish Paran <kparan@codeaurora.org>