src/post2meta: gensub argument fix

Older versions of Gawk did not mind an empty string as the third
argument, but newer versions complain:

  warning: gensub: third argument `' treated as 1

src/post2meta

@@ -34,7 +34,7 @@ BEGINFILE {
     print "author: Mike Gerwitz <mtg@gnu.org>"
 
     printf "date: %s\n",
-        gensub( /^(.{10}).*$/, "\\1", "", name[0] )
+        gensub( /^(.{10}).*$/, "\\1", 1, name[0] )
 }
 
 # Wait until after <main>; everything before it is the HTML header.
@@ -53,7 +53,7 @@ main && /^<h1 / {
     printf "slug: %s\n", \
         gensub( /^([0-9]+)-([0-9]+)-[0-9]+-(.*)\.[a-z]+$/,
                 "\\1/\\2/\\3",
-                "",
+                1,
                 name[0] )
 
     # Skip the date line immediately following the header and grab the first