Fix checker crash with new block scoped bindings

Signed-off-by: Joey Watts <jwatts43@bloomberg.net>

Author: Joey Watts

src/compiler/checker.ts

@@ -17721,6 +17721,7 @@ namespace ts {
                 // mark variables that are declared in loop initializer and reassigned inside the body of ForStatement.
                 // if body of ForStatement will be converted to function then we'll need a extra machinery to propagate reassigned values back.
                 if (container.kind === SyntaxKind.ForStatement &&
+                    symbol.valueDeclaration.kind === SyntaxKind.VariableDeclaration &&
                     getAncestor(symbol.valueDeclaration, SyntaxKind.VariableDeclarationList)!.parent === container &&
                     isAssignedInBodyOfForStatement(node, <ForStatement>container)) {
                     getNodeLinks(symbol.valueDeclaration).flags |= NodeCheckFlags.NeedsLoopOutParameter;