IsolatedStorageException (#18770)

* IsolatedStorageException

IsolatedStorageException thrown on CreateFile if path contains a Directory that does not exist.

* Update how-to-create-files-and-directories-in-isolated-storage.md

Co-authored-by: Andy De George <[email protected]>

Author: OzBob

docs/standard/io/how-to-create-files-and-directories-in-isolated-storage.md

@@ -23,6 +23,8 @@ After you have obtained an isolated store, you can create directories and files
  To create a file, use  the <xref:System.IO.IsolatedStorage.IsolatedStorageFile.CreateFile%2A?displayProperty=nameWithType> method.  
 
  In the Windows operating system, isolated storage file and directory names are case-insensitive. That is, if you create a file named `ThisFile.txt`, and then create another file named `THISFILE.TXT`, only one file is created. The file name keeps its original casing for display purposes.  
+
+ Isolated storage file creation will throw an <xref:System.IO.IsolatedStorage.IsolatedStorageException> if the path contains a directory that does not exist.
 
 ## Example  
  The following code example illustrates how to create files and directories in an isolated store.