Fix NPE in DeviceMediaLoader when device media title is null (#23131)

MediaColumns.TITLE can be null for some device media entries, which
crashed the media loader when constructing DeviceMediaItem. Make the
title nullable and show "Unknown" when representing an item without a
name.

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

Author: adalpari

WordPress/src/main/java/org/wordpress/android/ui/mediapicker/MediaPickerViewModel.kt

@@ -253,7 +253,7 @@ class MediaPickerViewModel @Inject constructor(
                     clickAction = clickAction
                 )
                 AUDIO, DOCUMENT -> MediaPickerUiItem.FileItem(
-                    fileName = it.name ?: "",
+                    fileName = it.name ?: resourceProvider.getString(R.string.unknown),
                     fileExtension = fileExtension,
                     identifier = it.identifier,
                     isSelected = isSelected,

WordPress/src/main/java/org/wordpress/android/ui/mediapicker/loader/DeviceMediaLoader.kt

@@ -153,7 +153,7 @@ class DeviceMediaLoader
 
     data class DeviceMediaList(val items: List<DeviceMediaItem>, val next: Long? = null)
 
-    data class DeviceMediaItem(val uri: UriWrapper, val title: String, val dateModified: Long)
+    data class DeviceMediaItem(val uri: UriWrapper, val title: String?, val dateModified: Long)
 
     companion object {
         private const val ID_COL = Media._ID