Make EXTRA_FOLDER key constant and guaranteed non-null

Minimal possible change to streamline the handling of this intent key.
Alternatively, the class.java.simpleName or the !! operator could've been
used at time of field definition. And the same would apply to several other
places as well.

Signed-off-by: Philipp Hasper <[email protected]>

Author: PhilLab

app/src/main/java/com/owncloud/android/ui/activity/FolderPickerActivity.kt

@@ -276,7 +276,7 @@ open class FolderPickerActivity :
         super.onResume()
         Log_OC.e(TAG, "onResume() start")
 
-        val extraFolder = intent.getParcelableArgument(EXTRA_FOLDER.toString(), OCFile::class.java)
+        val extraFolder = intent.getParcelableArgument(EXTRA_FOLDER, OCFile::class.java)
         if (extraFolder != null) {
             file = extraFolder
         } else {
@@ -658,8 +658,7 @@ open class FolderPickerActivity :
     }
 
     companion object {
-        @JvmField
-        val EXTRA_FOLDER = FolderPickerActivity::class.java.canonicalName?.plus(".EXTRA_FOLDER")
+        const val EXTRA_FOLDER = "com.owncloud.android.ui.activity.FolderPickerActivity".plus(".EXTRA_FOLDER")
 
         @JvmField
         @Deprecated(