undo parallel loop (#716)

This caused errors during rewriting to be obfuscated with null reference exceptions.

docs/release-notes.md

@@ -6,7 +6,6 @@
   * Mod warnings are now listed alphabetically.
   * MacOS files starting with `._` are now ignored and can no longer cause skipped mods.
   * Simplified paranoid warning logs and reduced their log level.
-  * Reduced startup time when loading mod DLLs (thanks to ZaneYork!).
   * Fixed `BadImageFormatException` error detection.
   * Fixed black maps on Android for mods which use `.tmx` files.
 

src/SMAPI/Framework/ModLoading/Framework/RecursiveRewriter.cs

@@ -57,11 +57,12 @@ namespace StardewModdingAPI.Framework.ModLoading.Framework
         /// <returns>Returns whether the module was modified.</returns>
         public bool RewriteModule()
         {
-            return this.Module.GetTypes().AsParallel().WithExecutionMode(ParallelExecutionMode.ForceParallelism).Select(type =>
+            bool anyRewritten = false;
+
+            foreach (TypeDefinition type in this.Module.GetTypes())
             {
-                bool anyRewritten = false;
                 if (type.BaseType == null)
-                    return false; // special type like <Module>
+                    continue; // special type like <Module>
 
                 anyRewritten |= this.RewriteCustomAttributes(type.CustomAttributes);
                 anyRewritten |= this.RewriteGenericParameters(type.GenericParameters);
@@ -107,9 +108,9 @@ namespace StardewModdingAPI.Framework.ModLoading.Framework
                         }
                     }
                 }
+            }
 
-                return anyRewritten;
-            }).Max();
+            return anyRewritten;
         }