Drop first recording buffer if it's from tizen allocator

- In single stream device, preview buffer is also used for recording,
  and the first recording buffer to appsrc is copied, because its reference count is bigger than 1.
  Dropping buffer will decrease reference count and avoid to copy it.

[Version] 0.10.168
[Profile] Common
[Issue Type] Update
[Dependency module] N/A
[Test] [M(T) - Boot=(OK), sdb=(OK), Home=(OK), Touch=(OK), Version=tizen-unified_20180903.2]

Change-Id: I658bf7822f62cb3f86a5749fe4dacc120bf44685
Signed-off-by: Jeongmo Yang <jm80.yang@samsung.com>