[3.12] GH-105588: Add missing error checks to some obj2ast_* converters (GH-105838)

GH-105588: Add missing error checks to some obj2ast_* converters (GH-105589)
(cherry picked from commit a4056c8f9c2d9970d39e3cb6bffb255cd4b8a42c)

Co-authored-by: Brandt Bucher <brandtbucher@microsoft.com>