fix 'doterrain menu bug'

From a report sent directly to devteam:  the #terrain command had the
same bug as the '`' command (which was one of the very first ones
reported):  impossible("add_menu called before start_menu").  Only X11
notices.

doc/fixes36.1

@@ -92,8 +92,8 @@ MacOSX: initial binary release was built from out of date source code that
 	had 'BETA' and 'DEBUG' inappropriately enabled
 MacOSX: force TIMED_DELAY build option on so that 'runmode' run-time option
 	is functional
-X11: core bug for '`' (backtick) command was only noticed by X11 interface,
-	which issued impossible message "add_menu: called before start_menu"
+X11: core bug for '`' (backtick) and #terrain commands was only noticed by
+	X11 interface: impossible "add_menu: called before start_menu"
 
 
 General New Features

src/cmd.c

@@ -1176,6 +1176,7 @@ doterrain(VOID_ARGS)
      *  a legend for the levl[][].typ codes dump
      */
     men = create_nhwindow(NHW_MENU);
+    start_menu(men);
     any = zeroany;
     any.a_int = 1;
     add_menu(men, NO_GLYPH, &any, 0, 0, ATR_NONE,