patch 8.0.1773: dialog messages are not translated

Problem:    Dialog messages are not translated.
Solution:   Add N_() and _() where needed. (Sergey Alyoshin)
diff --git a/src/ex_cmds2.c b/src/ex_cmds2.c
index 69283d6..7fa4907 100644
--- a/src/ex_cmds2.c
+++ b/src/ex_cmds2.c
@@ -4140,7 +4140,8 @@
 	char_u *fname = NULL;
 
 	fname = do_browse(0, (char_u *)_("Source Vim script"), eap->arg,
-				      NULL, NULL, BROWSE_FILTER_MACROS, NULL);
+				      NULL, NULL,
+				      (char_u *)_(BROWSE_FILTER_MACROS), NULL);
 	if (fname != NULL)
 	{
 	    cmd_source(fname, eap);