Fix failing test case where uri.host was null.

Font names are passed in without a host name or protocol, so
trying to use `uri.host` was resulting in "null" being inserted
into the path. This fixes that by checking whether `uri.host` is
falsey before using it.

Also, it was getting hard to read, so factored out some
expressions into their own variables.

lib/middleware.js

@@ -18,7 +18,9 @@ middleware.normalizePaths = function(req, res, next) {
         if (!req.query[key]) return;
         var uri = tm.parse(req.query[key]);
         var is_windows = (req.query[key].indexOf(':\\') >= 0);
-        req.query[key] = (uri.protocol ? uri.protocol + '//' : '') + (is_windows ? '' : uri.host) + uri.dirname;
+        var protocol = uri.protocol ? uri.protocol + '//' : '';
+        var host = (is_windows || !uri.host) ? '' : uri.host;
+        req.query[key] = protocol + host + uri.dirname;
     });
     ['id','source'].forEach(function(key) {
         if (!req.body || !req.body[key]) return;
@@ -28,7 +30,9 @@ middleware.normalizePaths = function(req, res, next) {
         // field, so we need to exclude the host from the normalised path
         // when we detect that it's a windows path.
         var is_windows = (req.body[key].indexOf(':\\') >= 0);
-        req.body[key] = (uri.protocol ? uri.protocol + '//' : '') + (is_windows ? '' : uri.host) + uri.dirname;
+        var protocol = uri.protocol ? uri.protocol + '//' : '';
+        var host = (is_windows || !uri.host) ? '' : uri.host;
+        req.body[key] = protocol + host + uri.dirname;
     });
     next();
 };