Fix duplicate contacts on autosave for addresses with uppercase letters

IncFrec() lowercases the existing addresses but compares them against the
new address in its original case, so an address with uppercase letters is
never found and a new contact is created on every send.

Fixes #1767

snappymail/v/0.0.0/app/libraries/RainLoop/Providers/AddressBook/PdoAddressBook.php

@@ -997,7 +997,7 @@ class PdoAddressBook
 					$sEmail = \trim($oItem->GetEmail(true));
 					if (\strlen($sEmail)) {
 						$aEmailsToUpdate[] = $sEmail;
-						return !\in_array($sEmail, $aExists);
+						return !\in_array(\mb_strtolower($sEmail), $aExists);
 					}
 				}
 				return false;