How to capture _fopen invalid (NULL) file handle?

I have two asm files: parse.asm, fileops.asm parse.exe accepts a file name in the command line argument. The file name is passed to fileops's global open_file method.

fileops implements _fopen to get a file handle. The application seems to be working fine (so far) for files that exist. However, the code fails with a file that does not exist ...which is what I am now trying to prevent.

Here is the fileops.open_file function:

open_file:
    ;   stash base stack pointer
    push    ebp
    mov     ebp,    esp

    mov     eax,        [ebp + 8]   ; location of
    mov     [fn],       eax         ; file name argument
    push    DWORD       [fn]     
    push    DWORD       mopf
    call    _printf                 ; displ: "[FILE] open: /file_name/"
    add     esp,    8

    ;   open file
    push    DWORD  fread            ; mode
    push    DWORD  [fn]
    call    _fopen                  ; how can I check for error here: e.g., file not found, etc.
    add     esp,    8

    push    DWORD   [eax]           ; push result to stack
    xor     eax,    eax             ; ret 0

    .done:
    ;   restore base stack pointer
    mov     esp,    ebp
    pop     ebp

    ret

My understanding is that in C, fopen(...) returns a NULL to the pointer. But then there is a GetLastError() that would give me a code or something that would tell me what the problem was. How can I implement this open_file?.

At the very least, I am okay with simply returning 1 in eax if the handle is invalid (0).