[BitcodeReader] Check vector size before trying to create a VectorType

Bug found with AFL fuzz

llvm-svn: 238891

llvm/lib/Bitcode/Reader/BitcodeReader.cpp

@@ -1497,6 +1497,8 @@ std::error_code BitcodeReader::ParseTypeTableBody() {
     case bitc::TYPE_CODE_VECTOR:    // VECTOR: [numelts, eltty]
       if (Record.size() < 2)
         return Error("Invalid record");
+      if (Record[0] == 0)
+        return Error("Invalid vector length");
       ResultTy = getTypeByID(Record[1]);
       if (!ResultTy || !StructType::isValidElementType(ResultTy))
         return Error("Invalid type");