Writes a block of bytes to the System.IO.IsolatedStorage.IsolatedStorageFileStream object using data read from a byte array.
The offset parameter gives the offset of the byte in the buffer at which to begin reading, and the count parameter gives the number of bytes that will be written to this System.IO.IsolatedStorage.IsolatedStorageFileStream object. If the write operation is successful, the current position of the System.IO.IsolatedStorage.IsolatedStorageFileStream object is advanced by the number of bytes written. If an exception occurs, the current position of the System.IO.IsolatedStorage.IsolatedStorageFileStream object is unchanged.