3a0e76fc12 Replace remaining 0 with nullptr in Qt code (Ben Woosley)
9096276e0b Don't use zero as null pointer constant (-Wzero-as-null-pointer-constant) (practicalswift)
Pull request description:
This corrects all violations of `-Wzero-as-null-pointer-constant` identified in the Qt codebase.
These changes are extracted from #15112 as suggested by @MarcoFalke to ease review. This is in service of enabling `-Wzero-as-null-pointer-constant`, which should eliminate this as a concern going forward.
Note there are 2 non-Qt changes: `src/test/allocator_tests.cpp` and `src/wallet/db.cpp`.
Tree-SHA512: 206bd668802147ba42bc413c2d7d259cb59aca9ec1da74a6bf2ca3932e60ae492faacbc61bcee0fd6b4b49a4d59d075b7e5404f0526b36c47718f9b0587e7768
76335298f4