Prevent GTK warnings when creating new account: Closes bgo#726269

The code for distinguishing between a new database and an existing
one being upgraded was faulty, causing the progress monitor to be
started/stopped when it should've have been.

src/engine/db/db-connection.vala

@@ -232,7 +232,11 @@ public class Geary.Db.Connection : Geary.Db.Context {
     }
     
     /**
-     * See set_user_version_number().
+     * Returns the user_version number maintained by SQLite.
+     *
+     * A new database has a user version number of zero.
+     *
+     * @see set_user_version_number().
      */
     public int get_user_version_number() throws Error {
         return get_pragma_int(PRAGMA_USER_VERSION);

src/engine/db/db-versioned-database.vala

@@ -77,8 +77,9 @@ public class Geary.Db.VersionedDatabase : Geary.Db.Database {
         debug("VersionedDatabase.upgrade: current database schema for %s: %d", db_file.get_path(),
             db_version);
         
-        // If the DB doesn't exist yet, the version number will be negative.
-        bool new_db = db_version < 0;
+        // If the DB doesn't exist yet, the version number will be zero, but also treat negative
+        // values as new
+        bool new_db = db_version <= 0;
         
         // Initialize new database to version 1 (note the preincrement in the loop below)
         if (db_version < 0)

src/engine/imap-db/imap-db-database.vala

@@ -47,6 +47,10 @@ private class Geary.ImapDB.Database : Geary.Db.VersionedDatabase {
         // can't call the ProgressMonitor directly, as it's hooked up to signals that expect to be
         // called in the foreground thread, so use the Idle loop for this
         Idle.add(() => {
+            // don't use upgrade_monitor for new databases, as the upgrade should be near-
+            // instantaneous.  Also, there's some issue with GTK when starting the progress
+            // monitor while GtkDialog's are in play:
+            // https://bugzilla.gnome.org/show_bug.cgi?id=726269
             if (!new_db && !upgrade_monitor.is_in_progress)
                 upgrade_monitor.notify_start();