I have sent a pull request here: #441

The patch removed the "Error: Locate graphic output protocol fail: (0xE) Not Found." message box.

If gop(Graphic Output Protocol) is not implemented in your platform, then a small window box will prompt and be waiting for a keystroke pressed by user, such that no more action can be implicitly continued thereafter. For example, VM cannot be accessed . There are 2 solutions:
[sol-1]
Following Joey's suggestion, we can just remove the warning window box generated by console_error() function.
efi_status = gBS->LocateProtocol(&gop_guid, NULL, (void **)&gop);
if (EFI_ERROR(efi_status)) {
console_error(L"Locate graphic output protocol fail", efi_status);
return;
}
[sol-2]
Let timer to control warning window box generated by console_countdown() function.
efi_status = gBS->LocateProtocol(&gop_guid, NULL, (void **)&gop);
if (EFI_ERROR(efi_status)) {
console_countdown(title,L"cannot find a graphic output protocol",timeout);
return;
}
Any comments are welcome :-)

Close this issue because patch be merged to shim mainline.