crecord: fix blue artifact bug coming back from help screen

Before this patch, with record's curses interface:
- When one pressed the ? key to see the help menu and then leaves the help menu
- Then, blue artifacts would remain on the screen

This patch forces a screen clear / refresh after coming back from the help menu.
Since we don't have UI test for crecord I checked on my machine that the bug
does not reproduce.

mercurial/crecord.py

@@ -1554,6 +1554,8 b' are you sure you want to review/edit and'
             self.togglefolded(foldparent=True)
         elif keypressed in ["?"]:
             self.helpwindow()
+            self.stdscr.clear()
+            self.stdscr.refresh()
 
     def main(self, stdscr):
         """