make Facebook preview icon conditional on the config parameter being …

…defined

Make sure $LJ::FACEBOOK_PREVIEW_ICON is defined in the config before
trying to include it.  Also straightens the indentation of the
previous line.

cgi-bin/LJ/S2.pm

@@ -2374,8 +2374,9 @@ sub Page
     # other useful link rels
     $p->{head_content} .= qq{<link rel="help" href="$LJ::SITEROOT/support/faq" />\n};
     $p->{head_content} .= qq{<link rel="apple-touch-icon" href="$LJ::APPLE_TOUCH_ICON" />\n}
-         if $LJ::APPLE_TOUCH_ICON;
-    $p->{head_content} .= qq{<meta property="og:image" content="$LJ::FACEBOOK_PREVIEW_ICON"/>\n};
+        if $LJ::APPLE_TOUCH_ICON;
+    $p->{head_content} .= qq{<meta property="og:image" content="$LJ::FACEBOOK_PREVIEW_ICON"/>\n}
+        if $LJ::FACEBOOK_PREVIEW_ICON;
     $p->{head_content} .= qq{<meta property="og:image:width" content="363"/>\n};
     $p->{head_content} .= qq{<meta property="og:image:height" content="363"/>\n};
     # Identity (type I) accounts only have read views