Don't sort an empty file list

sort just waits for stdin forever

Closes #1

Bug: T145534

lib/fileParser.js

@@ -103,6 +103,9 @@ function parseSourceFile(srcFile, zoomLevels, zoomLvlIndex, cleanupList) {
 }
 
 function sortFile(files, cleanupList) {
+    if (files.length === 0) {
+        throw new Err('sortFile() called with empty file list');
+    }
     return tmp.tmpName({prefix: 'tilerator-sorted-'}).then(function (dstFile) {
 
         cleanupList.push(dstFile);
@@ -268,6 +271,12 @@ function fileParser(filepath, options, addJobCallback) {
                     }
                     lastParsedFile = filepath[i];
                 }
+
+                if (tempFiles2.length === 0) {
+                    core.log('info', 'All tiles filtered out, nothing to process');
+                    process.exit();
+                }
+
                 return sortFile(tempFiles2, cleanupList);
             }).then(function (sortedFile) {
                 cleanupList.push(sortedFile);

package.json

@@ -1,6 +1,6 @@
 {
   "name": "tilerator-jobprocessor",
-  "version": "0.0.10",
+  "version": "0.0.11",
   "description": "Processes tile generation jobs",
   "main": "index.js",
   "scripts": {