[PATCH 4/7] windowscodecs: Introduce is_compressed(). And fix some format checks.

[Ziqing Hui]

Signed-off-by: Ziqing Hui <zhui(a)codeweavers.com>
---
 dlls/windowscodecs/ddsformat.c       | 37 ++++++++++++++++++++++------
 dlls/windowscodecs/tests/ddsformat.c |  5 ++--
 2 files changed, 31 insertions(+), 11 deletions(-)