Messy diff

[Johan Gill]

I found that there were problems with --debugmsg=+relay when hitting a
function call with an invalid pointer as parameter. wine_dbgstr_an() would
try to dereference the pointer, resulting in a crash.

Here's a patch for it. If anything is done the wrong way, please comment
on it.

/Johan Gill, johane(a)lysator.liu.se