Simplify volumeInfo retrieval code in unmount

In the current code, if |entry| is not null and |volumeInfo| is null,
the code will throw an exception.

Bug: 989364
Change-Id: Iae24eeabadd0d99f83fab8feb8cfbf3870723edf
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1727829Reviewed-by: Noel Gordon <noel@chromium.org>
Commit-Queue: Austin Tankiang <austinct@chromium.org>
Cr-Commit-Position: refs/heads/master@{#682605}

ui/file_manager/file_manager/foreground/js/file_manager_commands.js

@@ -599,14 +599,18 @@ CommandHandler.COMMANDS_['unmount'] = new class extends Command {
     const volumeInfo =
         CommandUtil.getElementVolumeInfo(event.target, fileManager);
     const entry = CommandUtil.getCommandEntry(fileManager, event.target);
-    if (!volumeInfo && !entry) {
+
+    let volumeType;
+    if (entry && entry instanceof EntryList) {
+      volumeType = entry.rootType;
+    } else if (volumeInfo) {
+      volumeType = volumeInfo.volumeType;
+    } else {
       event.canExecute = false;
       event.command.setHidden(true);
       return;
     }
 
-    const volumeType =
-        (entry instanceof EntryList) ? entry.rootType : volumeInfo.volumeType;
     event.canExecute =
         (volumeType === VolumeManagerCommon.VolumeType.ARCHIVE ||
          volumeType === VolumeManagerCommon.VolumeType.REMOVABLE ||