[NFC][CLANG] Fix issue with dereference null return value found by Coverity
Reported by Static Analyzer Tool, Coverity:
Inside "SemaDeclCXX.cpp" file, in clang::Sema::CheckExplicitlyDefaultedSpecialMember(clang::CXXMethodDecl *, clang::Sema::CXXSpecialMember, clang::SourceLocation): Return value of function which returns null is dereferenced without checking.
//returned_null: getAs returns nullptr (checked 117 out of 143 times).
// var_assigned: Assigning: Type = nullptr return value from getAs.
const FunctionProtoType *Type = MD->getType()->getAs<FunctionProtoType>();
//Dereference null return value (NULL_RETURNS)
//dereference: Dereferencing a pointer that might be nullptr Type when calling getReturnType.
ReturnType = Type->getReturnType();
//Dereference null return value (NULL_RETURNS)
//dereference: Dereferencing a pointer that might be nullptr Type when calling getParamType.
QualType ArgType = ExpectedParams ? Type->getParamType(0) : QualType();
This patch uses castAs instead of getAs which will assert if the type doesn't match.
Reviewed By: erichkeane
Differential Revision: https://reviews.llvm.org/D151281