msi: prevent cryptical errors

[Alexandre Julliard]

André Hentschel <nerv at dawncrow.de> writes:

> when accidently using the wrong path then
> 	err:msi:MSI_OpenPackageW can't find L"asf.msi"
> is more readable than
> 	err:msi:copy_package_to_temp failed to copy package L"asf.msi" to L"C:\\users\\dawncrow\\Temp\\msi71e7.tmp" (2)

Then you should fix that function to display a better error, instead of
adding an extra check to every open.

-- 
Alexandre Julliard
julliard at winehq.org