fix warning in cJSON.c

easyflash/plugins/types/struct2json/src/cJSON.c

@@ -276,8 +276,8 @@ static char *print_string_ptr(const char *str,printbuffer *p)
 		strcpy(out,"\"\"");
 		return out;
 	}
-	ptr=str;while ((token=*ptr) && ++len) {if (strchr("\"\\\b\f\n\r\t",token)) len++; else if (token<32) len+=5;ptr++;}
     
+	ptr=str;while (('\0' != (token=*ptr)) && ++len) {if (NULL != strchr("\"\\\b\f\n\r\t",token)) len++; else if (token<32) len+=5;ptr++;}
 	if (p)	out=ensure(p,len+3);
 	else	out=(char*)cJSON_malloc(len+3);
 	if (!out) return 0;