Get(/Thread)ErrorMode: Add missing possible return value

[nir9]

Copied the meaning of the zero return value from SetErrorMode, the following code verifies this:

#include <windows.h>
#include <stdio.h>

int main()
{
	SetErrorMode(0); // or SetThread..
	printf("the error mode is %d\n", GetErrorMode()); // or GetThread..
}

[prmerger-automator]

@nir9 : Thanks for your contribution! The author(s) have been notified to review your proposed change.