fix: Avoid crash when \operatorname has \limits (#2979)

test/katex-spec.js

@@ -2852,6 +2852,8 @@ describe("operatorname support", function() {
         expect("\\operatorname*{x*Π∑\\Pi\\sum\\frac a b}").toBuild();
         expect("\\operatorname*{x*Π∑\\Pi\\sum\\frac a b}_y x").toBuild();
         expect("\\operatorname*{x*Π∑\\Pi\\sum\\frac a b}\\limits_y x").toBuild();
+        // The following does not actually render with limits. But it does not crash either.
+        expect("\\operatorname{sn}\\limits_{b>c}(b+c)").toBuild();
     });
 });