rcfile: when a keystroke is rebound, don't bother unbinding it

The new binding will be put at the head of the list and thus will
be the one that is found -- the old binding will never be seen, so
rubbing it out is just a waste of time.

src/rcfile.c

@@ -468,11 +468,13 @@ void parse_binding(char *ptr, bool dobind)
 		}
 	}
 
-	/* Now find and delete any existing same shortcut in the menu(s). */
+	if (!dobind) {
+		/* Find and wipe the given shortcut from the given menu. */
 	for (s = sclist; s != NULL; s = s->next) {
 		if ((s->menus & menu) && !strcmp(s->keystr, keycopy))
 			s->menus &= ~menu;
 	}
+	}
 
 	if (dobind) {
 #ifndef NANO_TINY