Never save Welcome as the mode to restore for sessions

With the recent fix for restoring the mode when restoring sessions
(0d10ecd6), it would save and later
restore Welcome mode when switching sessions on Welcome mode.

Change-Id: I285dc1f25734b8358ca04cfdb887aafa93576c3d
Reviewed-by: Daniel Teske <daniel.teske@theqtcompany.com>

src/plugins/projectexplorer/session.cpp

@@ -178,7 +178,8 @@ bool SessionManager::isDefaultSession(const QString &session)
 
 void SessionManager::saveActiveMode(IMode *mode)
 {
-    setValue(QLatin1String("ActiveMode"), mode->id().toString());
+    if (mode->id() != Id(Core::Constants::MODE_WELCOME))
+        setValue(QLatin1String("ActiveMode"), mode->id().toString());
 }
 
 void SessionManager::clearProjectFileCache()