indexer crash

Hi,

Because I was getting segfaults in libc in calloc calls by the indexer process of Dovecot 2.3.16, I ran indexer with valgrind to look for possible memory corruption. It did indeed find that indexer was accessing memory that had already been freed, I've attached the log file.

I've then tried running Dovecot with the fix in commit 97367ef61784a364ccf615cb816be6492329050d, but that didn't make any difference. Reverting (just the code in src/indexer) to the last revision before the recent rewrite to use connection.c (d76761698a06bab60a741c6794252fddec4292ef) did: valgrind doesn't log any errors anymore, and indexer has stopped crashing.

Onno