Fix T40157: Loading movies larger than 4GB in size fails

Issue was caused by _wstat returning EOVERFLOW error because
of file size didn't fit into stat structure which was using
long datatype.

The idea of this patch is to use _wstat64 and _stat64 structure
which is capable storing 64bit file sizes.

Made it a typedef for stat structure used by BLI_stat function
in order to make code easier to follow and avoid ifdefs all
over the place.

Additionally solved issue with BLI_exists which was wrongly
returning False in cases destination file is larger then 4GB.

source/blender/blenlib/BLI_fileops.h

@@ -59,7 +59,18 @@ int    BLI_rename(const char *from, const char *to);
 int    BLI_delete(const char *path, bool dir, bool recursive);
 int    BLI_move(const char *path, const char *to);
 int    BLI_create_symlink(const char *path, const char *to);
-int    BLI_stat(const char *path, struct stat *buffer);
+
+#ifdef WIN32
+#  ifndef __MINGW64__
+typedef struct _stat64 BLI_stat_t;
+#  else
+typedef struct stat BLI_stat_t;
+#endif
+#else
+typedef struct stat BLI_stat_t;
+#endif
+
+int    BLI_stat(const char *path, BLI_stat_t *buffer);
 
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