Skip null file in media library.

Looks like Samsung still returns 'null' here sometimes - for whatever reason.

app/src/main/AndroidManifest.xml

@@ -24,7 +24,7 @@ THE SOFTWARE.
 <manifest xmlns:android="http://schemas.android.com/apk/res/android"
 	package="ch.blinkenlights.android.vanilla"
 	android:versionName="1.1.0"
-	android:versionCode="11000"
+	android:versionCode="11001"
 	android:installLocation="auto">
 	<uses-permission android:name="android.permission.WAKE_LOCK" />
 	<uses-permission android:name="android.permission.FOREGROUND_SERVICE" />

app/src/main/java/ch/blinkenlights/android/medialibrary/MediaLibrary.java

@@ -171,6 +171,10 @@ public class MediaLibrary  {
 			defaultPaths.add(Environment.getExternalStorageDirectory().getAbsolutePath());
 
 			for (File file : context.getExternalMediaDirs()) {
+				// Returns 'null' on some Samsung devices?!.
+				if (file == null)
+					continue;
+
 				defaultPaths.add(file.getAbsolutePath());
 				// Check if we have access to a subdir which contains the 'Music' folder.
 				while ( (file = file.getParentFile()) != null) {