user: fix DrawTextExA/W on empty strings.

[Rein Klazes]

On Fri, 27 Jan 2006 10:28:04 -0800, you wrote:

>(Apart from the other discussion) are you sure that you really 
>mean that?
>"If the length is explicitly stated to be zero then don't do the 
>calcrect but if the length is to be measured and happens to come 
>out as zero then do do the calcrect"
>If so then I suggest at least a comment that it is deliberate; it 
>sounds counterintuitive to me.

I thought I did even better by providing tests for each of those cases,
which pass here under Win2k and XP.

Other weird observations: the different behavior of the A and W
functions; the "return 0" in that code are actually "return 1" on Win2k
but not on XP. 

Rein.