Fix NDX file creation when votes are included in QWK packets

When both Indexes (NDX files) and vote messages are included in a QWK packet (an unexpected, but valid combination), the "Record number" stored in NDX files for subs with votes would be incorrect as it did not increment when a vote message (with no body text) was added to the messages.dat file.

Reported by user that was trying to use MultiMail to read a QWK packet that included both votes and indexes and "IgnoreNDX: No" in their .mmailrc file.