Fetching ntdll symbols for syscall auto-generation failing

Similar to #2126, I think, but for a different version (1903).

When running Dr Memory, I get the following output:
```
~~Dr.M~~ Dr. Memory version 2.2.0
~~Dr.M~~ Running "build\Debug\SingularityTrainer.exe"
~~Dr.M~~ Running on an unsupported operating system version: WinVer=105;Rel=1903;Build=18362;Edition=Core. Exiting to trigger auto-generation of system call information. Re-run with -ignore_kernel to attempt to continue instead.
WARNING: Running on an unsupported operating system version. Attempting to auto-generate system call information...
drsys_find_sysnum_libs: C:\WINDOWS\system32\ntdll.dll is readable
drsys_find_sysnum_libs: C:\WINDOWS\system32\kernelbase.dll is readable
drsys_find_sysnum_libs: C:\WINDOWS\system32\kernel32.dll is readable
drsys_find_sysnum_libs: C:\WINDOWS\system32\gdi32.dll is readable
drsys_find_sysnum_libs: C:\WINDOWS\system32\imm32.dll is readable
drsys_find_sysnum_libs: C:\WINDOWS\system32\user32.dll is readable
drsys_find_sysnum_libs: C:\WINDOWS\system32\win32u.dll is readable
drsys_find_sysnum_libs: C:\WINDOWS\system32\ntdll.dll is readable
drsys_find_sysnum_libs: C:\WINDOWS\system32\kernelbase.dll is readable
drsys_find_sysnum_libs: C:\WINDOWS\system32\kernel32.dll is readable
drsys_find_sysnum_libs: C:\WINDOWS\system32\gdi32.dll is readable
drsys_find_sysnum_libs: C:\WINDOWS\system32\imm32.dll is readable
drsys_find_sysnum_libs: C:\WINDOWS\system32\user32.dll is readable
drsys_find_sysnum_libs: C:\WINDOWS\system32\win32u.dll is readable
Symbol cache directory is "D:\Programs\DrMemory\drmemory\logs\symcache"
Fetching symbols for "C:\WINDOWS\system32\ntdll.dll", attempt #0
Ignoring local _NT_SYMBOL_PATH in next attempt.
Fetching symbols for "C:\WINDOWS\system32\ntdll.dll", attempt #1
Ignoring local _NT_SYMBOL_PATH in next attempt.
Failed to fetch symbols for C:\WINDOWS\system32\ntdll.dll: error 1
~~Dr.M~~ WARNING: application exited with abnormal code 0xc000a004
```