Allow Drivers to handle key events after being restarted (#1150)

src/textual/drivers/linux_driver.py

@@ -176,6 +176,7 @@ class LinuxDriver(Driver):
                 self.exit_event.set()
                 if self._key_thread is not None:
                     self._key_thread.join()
+                self.exit_event.clear()
                 termios.tcflush(self.fileno, termios.TCIFLUSH)
         except Exception as error:
             # TODO: log this

src/textual/drivers/windows_driver.py

@@ -84,6 +84,7 @@ class WindowsDriver(Driver):
                 if self._event_thread is not None:
                     self._event_thread.join()
                     self._event_thread = None
+                self.exit_event.clear()
         except Exception as error:
             # TODO: log this
             pass