Update pidfile.py

Return directly in the `except` instead of checking again for zero (as suggested by @benoitc and @tilgovi)

gunicorn/pidfile.py

@@ -67,11 +67,8 @@ def validate(self):
         try:
             with open(self.fname, "r") as f:
                 try:
-                    wpid = int(f.read())
+                    wpid = int(f.read() or 0)
                 except ValueError:
-                    wpid = 0
-
-                if wpid <= 0:
                     return
 
                 try: