wmaker: update error message to have only one string to be translated

As a previous patch modified some instances of the error message to include
more information to the user, it is a good idea to update also the other
uses of the message, so that:
 - people helping on translation will have less messages to translate
 - this mean we provide more information to the user in these places too,
which can help him solve the problem

Signed-off-by: Christophe CURIS <christophe.curis@free.fr>
Signed-off-by: Carlos R. Mafra <crmafra@gmail.com>

po/zh_CN.po

@@ -990,8 +990,8 @@ msgstr "%s:不能打开或预处理菜单文件"
 
 #: ../src/rootmenu.c:1126 ../src/rootmenu.c:1227
 #, c-format
-msgid "%s:could not open menu file"
-msgstr "%s:不能打开菜单文件"
+msgid "could not open menu file \"%s\": %s"
+msgstr "不能打开菜单文件 \"%s\": %s"
 
 #: ../src/rootmenu.c:1153
 #, c-format