another SkSL crash fix

src/sksl/SkSLParser.cpp

 /*
  * Copyright 2016 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
  
 #include "stdio.h"
 #include "SkSLParser.h"
 #include "SkSLToken.h"
@@ skipping 313 matching lines @@
     }
     std::vector<Type::Field> fields;
     while (this->peek().fKind != Token::RBRACE) {
         std::unique_ptr<ASTVarDeclarations> decl = this->varDeclarations();
         if (!decl) {
             return nullptr;
         }
         for (const auto& var : decl->fVars) {
             auto type = (const Type*) fTypes[decl->fType->fName];
             for (int i = (int) var.fSizes.size() - 1; i >= 0; i--) {
-                if (var.fSizes[i]->fKind != ASTExpression::kInt_Kind) {
+                if (!var.fSizes[i] || var.fSizes[i]->fKind != ASTExpression::kInt_Kind) {
                     this->error(decl->fPosition, "array size in struct field must be a constant");
+                    return nullptr;
                 }
                 uint64_t columns = ((ASTIntLiteral&) *var.fSizes[i]).fValue;
                 std::string name = type->name() + "[" + to_string(columns) + "]";
                 type = new Type(name, Type::kArray_Kind, *type, (int) columns);
                 fTypes.takeOwnership((Type*) type);
             }
             fields.push_back(Type::Field(decl->fModifiers, var.fName, type));
             if (var.fValue) {
                 this->error(decl->fPosition, "initializers are not permitted on struct fields");
             }
@@ skipping 1098 matching lines @@
 bool Parser::identifier(std::string* dest) {
     Token t;
     if (this->expect(Token::IDENTIFIER, "identifier", &t)) {
         *dest = t.fText; 
         return true;
     }
     return false;
 }
 
 } // namespace