[FIX JENKINS-43228] Consider time zone for cron validation

(cherry picked from commit 43d612f9)

core/src/main/java/hudson/scheduler/CronTab.java

@@ -532,4 +532,17 @@ public final class CronTab {
             return null;
         }
     }
+
+    /**
+     * Returns the configured time zone, or null if none is configured
+     *
+     * @return the configured time zone, or null if none is configured
+     * @since TODO
+     */
+    @CheckForNull public TimeZone getTimeZone() {
+        if (this.specTimezone == null) {
+            return null;
+        }
+        return TimeZone.getTimeZone(this.specTimezone);
+    }
 }

core/src/main/java/hudson/scheduler/CronTabList.java

@@ -131,7 +131,7 @@ public final class CronTabList {
     public @CheckForNull Calendar previous() {
         Calendar nearest = null;
         for (CronTab tab : tabs) {
-            Calendar scheduled = tab.floor(Calendar.getInstance());
+            Calendar scheduled = tab.floor(tab.getTimeZone() == null ? Calendar.getInstance() : Calendar.getInstance(tab.getTimeZone()));
             if (nearest == null || nearest.before(scheduled)) {
                 nearest = scheduled;
             }
@@ -143,7 +143,7 @@ public final class CronTabList {
     public @CheckForNull Calendar next() {
         Calendar nearest = null;
         for (CronTab tab : tabs) {
-            Calendar scheduled = tab.ceil(Calendar.getInstance());
+            Calendar scheduled = tab.ceil(tab.getTimeZone() == null ? Calendar.getInstance() : Calendar.getInstance(tab.getTimeZone()));
             if (nearest == null || nearest.after(scheduled)) {
                 nearest = scheduled;
             }