Check whether EvaluatedStmt::Value is valid in VarDecl::hasInit (llvm#94515)

VarDecl::isNull() doesn't tell whether the VarDecl has an initializer as
methods like ensureEvaluatedStmt can create an EvaluatedStmt even when
there isn't an initializer.

Revert e1c3e16 as the change isn't
needed anymore with this change.

See the discussion in llvm#93749.

Author: ahatanak

clang/lib/AST/Decl.cpp

@@ -2390,6 +2390,9 @@ bool VarDecl::hasInit() const {
     if (P->hasUnparsedDefaultArg() || P->hasUninstantiatedDefaultArg())
       return false;
 
+  if (auto *Eval = getEvaluatedStmt())
+    return Eval->Value.isValid();
+
   return !Init.isNull();
 }
 
@@ -2402,10 +2405,8 @@ Expr *VarDecl::getInit() {
 
   auto *Eval = getEvaluatedStmt();
 
-  return cast_if_present<Expr>(
-      Eval->Value.isOffset()
-          ? Eval->Value.get(getASTContext().getExternalSource())
-          : Eval->Value.get(nullptr));
+  return cast<Expr>(Eval->Value.get(
+      Eval->Value.isOffset() ? getASTContext().getExternalSource() : nullptr));
 }
 
 Stmt **VarDecl::getInitAddress() {