histedit: don't assign to _ for unused values

I don't know what this ignored value is, but we need to not clobber
the _() function from gettext, or we get mysterious crashes instead of
internationalizing some strings in my upcoming patches.

Differential Revision: https://phab.mercurial-scm.org/D9853

hgext/histedit.py

@@ -1615,7 +1615,7 b' pgup/K: move patch up, pgdn/J: move patc'
     stdscr.refresh()
     while True:
         try:
-            oldmode, _ = state[b'mode']
+            oldmode, unused = state[b'mode']
             if oldmode == MODE_INIT:
                 changemode(state, MODE_RULES)
             e = event(state, ch)
@@ -1630,7 +1630,7 b' pgup/K: move patch up, pgdn/J: move patc'
                     if size != stdscr.getmaxyx():
                         curses.resizeterm(*size)
 
-                curmode, _ = state[b'mode']
+                curmode, unused = state[b'mode']
                 sizes = layout(curmode)
                 if curmode != oldmode:
                     state[b'page_height'] = sizes[b'main'][0]