Merge #10265: [wallet] [moveonly] Check non-null pindex before potentially referencing

Summary:
c36ea69 [wallet] Make sure pindex is non-null before possibly referencing in LogPrintf call. (Karl-Johan Alm)

Tree-SHA512: a14c9f3e1228bca91977bea821c56a377d80889b41d250050c9be67aa93e460319a7cf1d4b63ee40f23b5a34159590f0e3fe15dc88698dc694c0c8098bd2db4d

Backport of Core PR 10265
https://github.com/bitcoin/bitcoin/pull/10265/files

Completes T643
Depends on D2976

Test Plan:
make check
test_runner.py

Reviewers: deadalnix, Fabien, #bitcoin_abc

Reviewed By: Fabien, #bitcoin_abc

Subscribers: markblundeberg

Differential Revision: https://reviews.bitcoinabc.org/D2974