Make glob optional in concats.js

Added:
- Condition to process includes with glob if it's available.

Changed:
- Utility 'glob.js' to not throw an error if a glob function is unavailable.

build/tasks/concats.js

@@ -56,21 +56,25 @@ export const productionConcatFilesArgs  = [
  * @todo Add support for minification.
  *
  * @async
- * @param  {object} [globOptions=null]   - Customize the glob options.
+ * @param  {object|boolean} [globOptions=null]   - Customize the glob options.
  *     If `null`, default production options are used.
+ *     If `false`, the glob function will be ignored.
  * @param  {object}         [concatOptions=null] - Customize the concatenation options.
  *     If `null`, default production options are used.
  * @return {Promise}
  */
 export default async function concatFiles(globOptions = null, concatOptions = null) {
+    if (glob) {
         if (globOptions == null) {
             globOptions = productionGlobOptions;
         } else if (
+            globOptions !== false &&
             globOptions !== developmentGlobOptions &&
             globOptions !== productionGlobOptions
         ) {
             globOptions = Object.assign({}, defaultGlobOptions, globOptions);
         }
+    }
 
     if (concatOptions == null) {
         concatOptions = productionConcatOptions;
@@ -97,7 +101,13 @@ export default async function concatFiles(globOptions = null, concatOptions = nu
             includes = includes.map((path) => template(path));
             outfile  = template(outfile);
 
-            let files = await glob(includes, globOptions);
+            let files;
+
+            if (glob && globOptions) {
+                files = await glob(includes, globOptions);
+            } else {
+                files = includes;
+            }
 
             if (concatOptions.removeDuplicates) {
                 files = files.map((path) => normalize(path));

build/utils/glob.js

@@ -22,7 +22,15 @@ const candidates = [
     'glob',
 ];
 
-export default await importGlob();
+let glob;
+
+try {
+    glob = await importGlob();
+} catch (err) {
+    // do nothing
+}
+
+export default glob;
 
 /**
  * Imports the first available glob function.