use a different function for getting screen size on kitkat

app/src/main/kotlin/com/simplemobiletools/gallery/activities/ViewPagerActivity.kt

@@ -402,9 +402,15 @@ class ViewPagerActivity : SimpleActivity(), ViewPager.OnPageChangeListener, View
 
     private fun measureScreen() {
         val metrics = DisplayMetrics()
+        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN_MR1) {
             windowManager.defaultDisplay.getRealMetrics(metrics)
             screenWidth = metrics.widthPixels
             screenHeight = metrics.heightPixels
+        } else {
+            windowManager.defaultDisplay.getMetrics(metrics)
+            screenWidth = metrics.widthPixels
+            screenHeight = metrics.heightPixels
+        }
     }
 
     private fun reloadViewPager() {