Fix base directory resolution for custom hosting environments

src/Loader/EnvLoader.HelperMethods.cs

@@ -72,7 +72,7 @@ private Result<string> GetEnvFilePath(string envFileName)
             envFileName = Path.GetFileName(envFileName);
         }
         else
-            path = AppContext.BaseDirectory;
+            path = PathResolver.BaseDirectory;
 
         for (var directoryInfo = new DirectoryInfo(path);
             directoryInfo is not null;

src/Loader/PathResolver.cs

@@ -0,0 +1,18 @@
+namespace DotEnv.Core;
+
+internal class PathResolver
+{
+    public static string BaseDirectory
+    {
+        get
+        {
+            // AppContext.BaseDirectory may not be available in all hosting
+            // environments (e.g. SampSharp/open.mp). Fall back to the current
+            // working directory when necessary.
+            if (!string.IsNullOrWhiteSpace(AppContext.BaseDirectory))
+                return AppContext.BaseDirectory;
+
+            return Directory.GetCurrentDirectory();
+        }
+    }
+}