fix(postcss-plugin): Skip css files without icons

Author: jantimon

lib/postcss-plugin.js

@@ -79,6 +79,10 @@ module.exports = postcss.plugin('iconfont-webpack', function (opts) {
     var context = path.dirname(cssFilename);
     return getSvgPaths(root, opts.compilation.compiler, context)
       .then(function (svgPaths) {
+        // Stop if the css file contains no `font-icon:url('..');` declarations
+        if (svgPaths.resolved.lenth === 0) {
+          return;
+        }
         // Generate a font icon name
         var md5sum = crypto.createHash('md5');
         md5sum.update(JSON.stringify(_.values(svgPaths.resolved)));