CRASH win10 app using legacy NtCreateProcessEx

I'm not sure whether this happens on any child process (surely that was well tested before) but the same app as in #1897 has a successfully child process creation that DR still crashes investigating:

```
?? &process_handle
void ** 0x1e49eb80
0:000> dd 0x1e49eb80 L1
1e49eb80 000000e4

00 1e49eb48 6bd12ee4 dynamorio!should_inject_into_process+0x270 [d:\derek\dr\git\src\core\win32\os.c @ 3031]
01 1e49eb74 6bd2d406 dynamorio!maybe_inject_into_process+0x134 [d:\derek\dr\git\src\core\win32\os.c @ 3233]
02 1e49ede0 6bb568ca dynamorio!post_system_call+0x1646 [d:\derek\dr\git\src\core\win32\syscall.c @ 4055]

inject_settings = 0x1e49eb80

0:000> dd 0x1e49eb80 L1
1e49eb80 00000000

back to maybe_inject_into_process frame:
0:000> ?? &should_inject
inject_setting_mask_t * 0x1e49eb80
0:000> ?? &process_handle
void ** 0x1e49eb80
```