Fixed the support for std::string which had regressed.
Fixed the support for std::string which had regressed.

Signed-off-by: Dimitar Dobrev <ca751a5c976abad79158718440750fc638d19ebc@protonmail.com>

genuinelucifer/CppSharp,u255436/CppSharp,ddobrev/CppSharp,genuinelucifer/CppSharp,mono/CppSharp,genuinelucifer/CppSharp,zillemarco/CppSharp,mohtamohit/CppSharp,ktopouzi/CppSharp,ktopouzi/CppSharp,mono/CppSharp,inordertotest/CppSharp,inordertotest/CppSharp,mono/CppSharp,ddobrev/CppSharp,ddobrev/CppSharp,zillemarco/CppSharp,mohtamohit/CppSharp,ktopouzi/CppSharp,ktopouzi/CppSharp,zillemarco/CppSharp,zillemarco/CppSharp,u255436/CppSharp,inordertotest/CppSharp,genuinelucifer/CppSharp,ktopouzi/CppSharp,ddobrev/CppSharp,inordertotest/CppSharp,genuinelucifer/CppSharp,zillemarco/CppSharp,u255436/CppSharp,ddobrev/CppSharp,mohtamohit/CppSharp,inordertotest/CppSharp,mono/CppSharp,u255436/CppSharp,mono/CppSharp,mohtamohit/CppSharp,mono/CppSharp,u255436/CppSharp,mohtamohit/CppSharp