crecord: extract most of 'main' into a sub function

There are some setup and cleanup necessary around the main code, that
setup/cleanup code needs multiple adjustments so we extract the core code into
its own function first for clarity.

mercurial/crecord.py

@@ -1616,6 +1616,10 b' are you sure you want to review/edit and'
 
         origsigwinchhandler = signal.signal(signal.SIGWINCH,
                                             self.sigwinchhandler)
+        return self._main(stdscr)
+        signal.signal(signal.SIGWINCH, origsigwinchhandler)
+
+    def _main(self, stdscr):
         self.stdscr = stdscr
         # error during initialization, cannot be printed in the curses
         # interface, it should be printed by the calling code
@@ -1667,4 +1671,3 b' are you sure you want to review/edit and'
                 keypressed = "foobar"
             if self.handlekeypressed(keypressed):
                 break
-        signal.signal(signal.SIGWINCH, origsigwinchhandler)