Stop converting null string arguments into empty strings

[ChrisThrasher]

Some APIs check will convert null const char* arguments to an empty string. I propose CSFML stop doing this except where the API actually promises that the behavior of null arguments is defined.

For example:

CSFML/src/CSFML/Network/Ftp.cpp

Lines 224 to 228 in 21d4571

	sfFtpResponse* sfFtp_login(sfFtp* ftp, const char* name, const char* password)
	{
	assert(ftp);
	return new sfFtpResponse{ftp->This.login(name ? name : "", password ? password : "")};
	}