[NFC][CLANG] Fix nullptr dereference issue in CodeGenModule::​GetConstantArrayFromStringLiteral()

[Manna]

Summary

This patch adds an assert.

[Manna]

Thank you @erichkeane for reviews!

clang/lib/CodeGen/CodeGenModule.cpp

CodeGenModule::GetConstantArrayFromStringLiteral(const StringLiteral *E) {
 
   // Don't emit it as the address of the string, emit the string data itself
   // as an inline array.
   if (E->getCharByteWidth() == 1) {
     SmallString<64> Str(E->getString());
 
     // Resize the string to the right size, which is indicated by its type.
     const ConstantArrayType *CAT = Context.getAsConstantArrayType(E->getType());
+    assert(CAT && "String literal not of constant array type!");
     Str.resize(CAT->getSize().getZExtValue());
     return llvm::ConstantDataArray::getString(VMContext, Str, false);
   }
 
   auto *AType = cast<llvm::ArrayType>(getTypes().ConvertType(E->getType()));
   llvm::Type *ElemTy = AType->getElementType();
   unsigned NumElements = AType->getNumElements();