block access to mod-provided APIs until all mods are initialised (#409)

src/SMAPI/Framework/ModHelpers/ModRegistryHelper.cs

@@ -70,6 +70,11 @@ namespace StardewModdingAPI.Framework.ModHelpers
         public TInterface GetApi<TInterface>(string uniqueID) where TInterface : class
         {
             // validate
+            if (!this.Registry.AreAllModsInitialised)
+            {
+                this.Monitor.Log("Tried to access a mod-provided API before all mods were initialised.", LogLevel.Error);
+                return null;
+            }
             if (!typeof(TInterface).IsInterface)
             {
                 this.Monitor.Log("Tried to map a mod-provided API to a class; must be a public interface.", LogLevel.Error);

src/SMAPI/Framework/ModRegistry.cs

@@ -18,6 +18,9 @@ namespace StardewModdingAPI.Framework
         /// <summary>An assembly full name => mod lookup.</summary>
         private readonly IDictionary<string, IModMetadata> ModNamesByAssembly = new Dictionary<string, IModMetadata>();
 
+        /// <summary>Whether all mods have been initialised and their <see cref="IMod.Entry"/> method called.</summary>
+        public bool AreAllModsInitialised { get; set; }
+
 
         /*********
         ** Public methods

src/SMAPI/Program.cs

@@ -842,6 +842,9 @@ namespace StardewModdingAPI
                 this.Monitor.Log("Invalidating cached assets for new editors & loaders...", LogLevel.Trace);
                 this.ContentManager.InvalidateCacheFor(editors, loaders);
             }
+
+            // unlock mod integrations
+            this.ModRegistry.AreAllModsInitialised = true;
         }
 
         /// <summary>Load a mod's entry class.</summary>