Reset buffer after stop protolog to file

After protolog-to-file stops, BaseProtoLogImpl.mBuffer still uses a lot of memory.

Bug: 262244460
Merged-In: If618dad902df3c7fc1b2a943fe550c7c34a2d65e
Change-Id: If618dad902df3c7fc1b2a943fe550c7c34a2d65e
1 file changed