assert for nullptr when passing to functions taking std::string_view implicitly.

[ZXShady]

in CSFML
sfIpAddress_fromString and sfContext_isExtentionAvaialable which takes a string view it is UB to pass nullptr as it is not a valid range see 4th constructor. so an assert checking for null before passing would help debug issues.

sfml function signatures
Context::isExtentionAvaiable

IpAddress::resolve