[lib] Simplify conditional logic in wrapActionPromise:loadingInfo

Summary: Noticed that some of the logic here could be simplified w/ optional chaining + nullish coalescing... so made those changes

Test Plan: Close reading + flow

Reviewers: palys-swm, def-au1t, yayabosh, ashoat

Reviewed By: palys-swm, yayabosh, ashoat

Subscribers: ashoat, Adrian

Differential Revision: https://phab.comm.dev/D4319