shm renderer: fix nullptr access
shm renderer: fix nullptr access

A nullptr deferencing could happen in ShmRenderer::currentFrame() method.
This patch tests the pointer value and returns an empty frame if this
pointer is null.

Issue: #81689
Change-Id: I4fba4f8efccfe49140d1d4b1a9d1027110c69d61

savoirfairelinux/ring-lrc,savoirfairelinux/ring-lrc,savoirfairelinux/ring-lrc,savoirfairelinux/ring-lrc,savoirfairelinux/ring-lrc