[geary: 1/2] engine: Allow zero UIDValidity value for IMAP

[Michael Gratton <mjog src gnome org>]

commit e55f0857bd688da40d5ed8598c64719aa8a163d7
Author: Thomas Lauerman <tom lauerman dev>
Date:   Sun Apr 4 18:44:49 2021 -0500

    engine: Allow zero UIDValidity value for IMAP
    
    At least one IMAP server has been observed to send a UIDVALIDITY 0 value,
    for example, iCloud. This change allows Geary to work with such servers,
    even though it's technically in violation of RFC 3501.
    
    Fixes #1183

 src/engine/imap/message/imap-uid-validity.vala | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)
---
diff --git a/src/engine/imap/message/imap-uid-validity.vala b/src/engine/imap/message/imap-uid-validity.vala
index 6f948cb1c..8fe2f849f 100644
--- a/src/engine/imap/message/imap-uid-validity.vala
+++ b/src/engine/imap/message/imap-uid-validity.vala
@@ -15,8 +15,12 @@
 public class Geary.Imap.UIDValidity : Geary.MessageData.Int64MessageData, Geary.Imap.MessageData {
     /**
      * Minimum valid value for a {@link UIDValidity}.
+     *
+     * This is smaller than the non-zero minimum RFC 3501 specifies, since at
+     * least one mail server has been observed to return zero values. See Issue
+     * #1183.
      */
-    public const int64 MIN = 1;
+    public const int64 MIN = 0;
 
     /**
      * Maximum valid value for a {@link UIDValidity}.