Write terminating strings when MsiGetFileVersion() fails.

I had expected that if you were returning a failure code you didn't
have to - perhaps even _shouldn't_ - write through the output pointer
arguments. But in fact, now that my implementation of
MsiGetFileVersion _knows_ how to fail (i.e. doesn't just return a
hardcoded value for every call), the MSI build doesn't work unless I
also clear the output strings in the case of failure.

fake-msi.c

@@ -25,6 +25,11 @@ uint32_t MsiGetFileVersionW(const char16_t *filename,
     int fd = -1;
     void *mapv = MAP_FAILED;
 
+    if (version && *version_size)
+        *version = 0;
+    if (language && *language_size)
+        *language = 0;
+
     fd = open(fname, O_RDONLY);
     if (fd < 0)
         err(1, "%s: open", fname);