Make sure to discard a draft whenever we're saving. Release-Notes: fixes deletion of patchset comment right before saving. Google-Bug-Id: b/309970044, b/309533366 Change-Id: I420fd0193f4911aca85b26989ebfa60f784f90d7 (cherry picked from commit 063fa5047dac347232e503ae8cc5b3aa15e68bdc)