Add initialization in case it is causing the Apple Clang release failure.

hlsl/hlslGrammar.cpp

@@ -2626,6 +2626,8 @@ bool HlslGrammar::acceptFunctionBody(TFunctionDeclarator& declarator, TIntermNod
 //
 bool HlslGrammar::acceptParenExpression(TIntermTyped*& expression)
 {
+    expression = nullptr;
+
     // LEFT_PAREN
     if (! acceptTokenClass(EHTokLeftParen))
         expected("(");
@@ -3674,7 +3676,6 @@ bool HlslGrammar::acceptIterationStatement(TIntermNode*& statement, const TAttri
         }
 
         // LEFT_PAREN condition RIGHT_PAREN
-        TIntermTyped* condition;
         if (! acceptParenExpression(condition))
             return false;
         condition = parseContext.convertConditionalExpression(loc, condition);