add a helper function to determine if the file is an image

library/src/main/kotlin/com/simplemobiletools/filepicker/models/FileDirItem.kt

@@ -1,5 +1,7 @@
 package com.simplemobiletools.filepicker.models
 
+import android.graphics.BitmapFactory
+
 class FileDirItem(val path: String, val name: String, val isDirectory: Boolean, val children: Int, val size: Long) :
         Comparable<FileDirItem> {
 
@@ -16,4 +18,10 @@ class FileDirItem(val path: String, val name: String, val isDirectory: Boolean,
     override fun toString(): String {
         return "FileDirItem{name=$name, isDirectory=$isDirectory, path=$path, children=$children, size=$size}"
     }
+
+    fun isImage(): Boolean {
+        val options = BitmapFactory.Options()
+        options.inJustDecodeBounds = true
+        return options.outWidth !== -1 && options.outHeight !== -1
+    }
 }