Add _is_debugger so load_dotenv will work in pdb (#553)

Author: randomseed42

src/dotenv/main.py

@@ -292,7 +292,10 @@ def _is_interactive():
             return False
         return not hasattr(main, "__file__")
 
-    if usecwd or _is_interactive() or getattr(sys, "frozen", False):
+    def _is_debugger():
+        return sys.gettrace() is not None
+
+    if usecwd or _is_interactive() or _is_debugger() or getattr(sys, "frozen", False):
         # Should work without __file__, e.g. in REPL or IPython notebook.
         path = os.getcwd()
     else: