Fix MSVC warnings in js.cpp

js/src/shell/js.cpp

@@ -2081,8 +2081,8 @@ Disassemble(JSContext *cx, uintN argc, jsval *vp)
     bool lines = false, recursive = false;
     while (argc > 0 && JSVAL_IS_STRING(argv[0])) {
         JSString *str = JSVAL_TO_STRING(argv[0]);
-        lines |= JS_MatchStringAndAscii(str, "-l");
-        recursive |= JS_MatchStringAndAscii(str, "-r");
+        lines |= !!JS_MatchStringAndAscii(str, "-l");
+        recursive |= !!JS_MatchStringAndAscii(str, "-r");
         if (!lines && !recursive)
             break;
         argv++, argc--;