Fix wrong conversation showing after QR scan (#520)

Skip inviteTag-based conversation matching when the tag is empty.
When a discovered XMTP group has an empty inviteTag (metadata not yet
synced or read failure), the query filter(inviteTag == "") would match
any existing conversation that also has an empty tag, causing the wrong
conversation's clientConversationId to be merged with the new group.

Author: yewreeka

ConvosCore/Sources/ConvosCore/Storage/Writers/ConversationWriter.swift

@@ -401,7 +401,8 @@ class ConversationWriter: ConversationWriterProtocol, @unchecked Sendable {
         // Apply the preserved timestamp
         var conversationToSave = dbConversation.with(imageLastRenewed: imageLastRenewed)
 
-        if let localConversation = try DBConversation
+        if !dbConversation.inviteTag.isEmpty,
+           let localConversation = try DBConversation
             .filter(DBConversation.Columns.inviteTag == dbConversation.inviteTag)
             .filter(DBConversation.Columns.clientConversationId != dbConversation.clientConversationId)
             .fetchOne(db) {