Auto merge of #1939 - str4d:1933-fix-bug, r=str4d

Only increment new notes on reindex

Addresses another issue in #1904.

When an existing one of our notes was found again, its cache was reset and it was re-witnessed. This would cause encountered notes to get out-of-sync with the otherwise-ignored newer notes, which could be a problem if the wallet data happens to be written out during a reindex.