Win32: Better Error Handling in BLI_file_attributes

After Win32 API call GetFileAttributesW, check for
INVALID_FILE_ATTRIBUTES, which is returned on error,
usually if file not found.

See D17176 for more details.

Differential Revision: https://developer.blender.org/D17176

Reviewed by Ray Molenkamp

source/blender/blenlib/intern/storage.c

@@ -209,7 +209,14 @@ eFileAttributes BLI_file_attributes(const char *path)
   if (conv_utf_8_to_16(path, wline, ARRAY_SIZE(wline)) != 0) {
     return ret;
   }
+
   DWORD attr = GetFileAttributesW(wline);
+  BLI_assert_msg(attr != INVALID_FILE_ATTRIBUTES,
+                 "BLI_file_attributes should only be called on existing files.");
+  if (attr == INVALID_FILE_ATTRIBUTES) {
+    return ret;
+  }
+
   if (attr & FILE_ATTRIBUTE_READONLY) {
     ret |= FILE_ATTR_READONLY;
   }