Merge some file writing extension checks from OpenJK.

Thanks Ensiform.
https://github.com/JACoders/OpenJK/commit/05928a57f9e4aae15a3bd0
https://github.com/JACoders/OpenJK/commit/ef124fd0fc48af164581176
static char *Field_FindFirstSeparator( char *s )
{
	int i;

	for( i = 0; i < strlen( s ); i++ )
	{
		if( s[ i ] == ';' )
			return &s[ i ];
	}

	return NULL;
}

static char *Field_FindFirstSeparator( char *s )
{
	int i;

	for( i = 0; i < strlen( s ); i++ )
	{
		if( s[ i ] == ';' )
			return &s[ i ];
	}

	return NULL;
}
