Fix a silly mistake in ComplexExprEvaluator::ZeroInitialization.  <rdar://problem/10691092>.

llvm-svn: 148157
diff --git a/clang/lib/AST/ExprConstant.cpp b/clang/lib/AST/ExprConstant.cpp
index 0cae138..912b111 100644
--- a/clang/lib/AST/ExprConstant.cpp
+++ b/clang/lib/AST/ExprConstant.cpp
@@ -4914,7 +4914,7 @@
 }
 
 bool ComplexExprEvaluator::ZeroInitialization(const Expr *E) {
-  QualType ElemTy = cast<ComplexType>(E->getType())->getElementType();
+  QualType ElemTy = E->getType()->getAs<ComplexType>()->getElementType();
   if (ElemTy->isRealFloatingType()) {
     Result.makeComplexFloat();
     APFloat Zero = APFloat::getZero(Info.Ctx.getFloatTypeSemantics(ElemTy));