A strong year for initial public offerings on Wall Street has fizzled out due to the government shutdown and a cautious turn by investors. Many IPOs targeted for the end of this year will likely be pushed into next year as the Securities and Exchange Commission works to clear a backlog of hundreds of registration statements. Meanwhile, shares of companies that did make their market debuts haven’t fared well lately amid concerns that stocks have gotten too expensive after another double-digit gain for the market this year.