Merge pull request #75 from rsnitsch/improve_get_children_performance

Speed up directory listing by factor 4-5 by improving getChildren function

app/src/main/kotlin/com/simplemobiletools/filemanager/fragments/ItemsFragment.kt

@@ -162,14 +162,15 @@ class ItemsFragment : Fragment(), ItemsAdapter.ItemOperationsListener {
     }
 
     private fun getChildren(file: File): Int {
-        if (file.listFiles() == null)
+        var fileList = file.list()
+        if (fileList == null)
             return 0
 
         if (file.isDirectory) {
             return if (mShowHidden) {
-                file.listFiles()?.size ?: 0
+                fileList.size
             } else {
-                file.listFiles { file -> !file.isHidden }?.size ?: 0
+                fileList.count { fileName -> fileName[0] != '.' }
             }
         }
         return 0