patch [#25490] Fix for [#22096] Blender tries to open non-blend file

from Alexander Kuznetsov (alexk) with edits.

From the report:
Blender assumed that all files are .blend as retval = 0;

Now retval is initialized as file cannot be open (-1) for gzopen fail and directory case
retval = -2; is defined for not supported formats
This must be assigned before #ifdef WITH_PYTHON because this part can be missing
Finally retval = 0; if it is a .blend file

---
also made other edits.

- exotic.c's blend header checking was sloppy, didn't check data was actually read, only checked first 4 bytes and had a check for "blend.gz" extension which is unnecessary.
- use defines to help readability for BKE_read_exotic & BKE_read_file return values.
- no need to check for a NULL pointer before calling BKE_reportf(). (will just print to the console)
- print better reports when the file fails to load.

1 files changed, 1 insertions, 1 deletions

diff --git a/source/creator/creator.c b/source/creator/creator.c
index 92da0fe5beb..5b994be2c06 100644
--- a/source/creator/creator.c
+++ b/source/creator/creator.c
@@ -904,7 +904,7 @@ static int load_file(int UNUSED(argc), char **argv, void *data)
 
 		/*we successfully loaded a blend file, get sure that
 		pointcache works */
-		if (retval!=0) {
+		if (retval != BKE_READ_FILE_FAIL) {
 			wmWindowManager *wm= CTX_wm_manager(C);
 
 			/* special case, 2.4x files */