fix issue where assemblies could be incorrectly reloaded

docs/release-notes.md

@@ -1,4 +1,8 @@
 # Release notes
+## 2.4
+* For players:
+  * Fixed rare issues caused by assembly references being incorrectly loaded twice.
+
 ## 2.3
 * For players:
   * Added a user-friendly [download page](https://smapi.io).

src/SMAPI/Framework/ModLoading/AssemblyLoader.cs

@@ -162,7 +162,11 @@ namespace StardewModdingAPI.Framework.ModLoading
 
             // skip if already visited
             if (visitedAssemblyNames.Contains(assembly.Name.Name))
+            {
                 yield return new AssemblyParseResult(file, null, AssemblyLoadStatus.AlreadyLoaded);
+                yield break;
+            }
+
             visitedAssemblyNames.Add(assembly.Name.Name);
 
             // yield referenced assemblies