Alerts crash fix (#26602)

- If the client tries to call ShowAlert while applying gamestates (e.g. initialising an entity) then this will cause problems. I need to double-check the initial PR before I'd be comfortable with this being merged.

(cherry picked from commit dd03612d80)

Content.Shared/Alert/AlertsSystem.cs

@@ -80,6 +80,10 @@ public abstract class AlertsSystem : EntitySystem
     /// <param name="showCooldown">if true, the cooldown will be visibly shown over the alert icon</param>
     public void ShowAlert(EntityUid euid, AlertType alertType, short? severity = null, (TimeSpan, TimeSpan)? cooldown = null, bool autoRemove = false, bool showCooldown = true )
     {
+        // This should be handled as part of networking.
+        if (_timing.ApplyingState)
+            return;
+
         if (!TryComp(euid, out AlertsComponent? alertsComponent))
             return;
 
@@ -148,6 +152,9 @@ public abstract class AlertsSystem : EntitySystem
     /// </summary>
     public void ClearAlert(EntityUid euid, AlertType alertType)
     {
+        if (_timing.ApplyingState)
+            return;
+
         if (!EntityManager.TryGetComponent(euid, out AlertsComponent? alertsComponent))
             return;