[1/2] msi/tests: Test MsiRecordGetString on null and empty strings.

[Nicolas Le Cam]

While trying to solve ACTION_AppSearchDr problem revealed by my previous
patch, I discovered that MSI_RecordGetStringW was returning a buffer
length of 1 on null and empty strings.

Here is the test, the fix follows.

Tested on WinXP and Wine.

--
Nicolas Le Cam