ledger: do not shadow db error in account lookup

[algorandskiy]

Summary

DB lookup might fail and acctupdates' lookup method return not original error but overwritten by another one.
This makes debugging a bit harder.

Test Plan

Existing tests

[codecov]

Codecov Report

Merging #4425 (996ffbf) into master (c1b6a03) will increase coverage by 0.03%.
The diff coverage is 46.15%.

@@            Coverage Diff             @@
##           master    #4425      +/-   ##
==========================================
+ Coverage   55.13%   55.16%   +0.03%     
==========================================
  Files         397      397              
  Lines       50073    50079       +6     
==========================================
+ Hits        27607    27627      +20     
+ Misses      20170    20156      -14     
  Partials     2296     2296              

Impacted Files	Coverage Δ
ledger/acctupdates.go	69.89% <46.15%> (-0.03%)	⬇️
ledger/blockqueue.go	85.63% <0.00%> (-2.88%)	⬇️
network/wsPeer.go	67.67% <0.00%> (ø)
network/wsNetwork.go	64.89% <0.00%> (ø)
catchup/service.go	69.38% <0.00%> (+0.49%)	⬆️
cmd/tealdbg/debugger.go	73.49% <0.00%> (+0.80%)	⬆️
crypto/merkletrie/node.go	93.48% <0.00%> (+1.86%)	⬆️
crypto/merkletrie/trie.go	68.61% <0.00%> (+2.18%)	⬆️
util/db/dbutil.go	48.48% <0.00%> (+4.24%)	⬆️
... and 1 more

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[jannotti]

Looks good - should give us the more important error detail.

[algorandskiy]

Fixed CR feedback

[jannotti]

Looks good