[proposal] fix assert for proposal builder

Tested: fx ota && check for (lack of) exceptions from krohnkite in the
logs.
Change-Id: Idb8f8f5e880c28dfcb0300a2423a3f08333251c4

Change-Id: Ib40353dd6f2a7d58806ce3d186ed8c33df0f8c44
2 files changed