bpo-30989: Sort in TimedRotatingFileHandler only when needed. (GH-2812) (GH-4466)

TimedRotatingFileHandler.getFilesToDelete() now sorts only when needed.
(cherry picked from commit afad147b59)

Lib/logging/handlers.py

@@ -356,10 +356,10 @@ class TimedRotatingFileHandler(BaseRotatingHandler):
                 suffix = fileName[plen:]
                 if self.extMatch.match(suffix):
                     result.append(os.path.join(dirName, fileName))
-        result.sort()
         if len(result) < self.backupCount:
             result = []
         else:
+            result.sort()
             result = result[:len(result) - self.backupCount]
         return result