Change useragent to something that doesn't get blocked (#1332)

* Change useragent to something that doesn't get blocked 

Looks like #1239 is still the case, with pixiv now blocking the current user agent, too. Switching it to the recommended value from 1239, however, works.

* Remove "dead" code

This also removes the code that got commented off in #1239, because either it's no longer need (so it doesn't need to be in the code at all) or it may be needed "sometimes" in which case it should probably live uncommented inside an `if` block.

* Link to the relevant README.md section

Added a link so people can easily get the information they need to fix the problem.

* (missing newline)

PixivConfig.py

@@ -57,8 +57,7 @@ class PixivConfig():
     __items = [
         ConfigItem("Network", "useProxy", False),
         ConfigItem("Network", "proxyAddress", ""),
-        ConfigItem("Network", "useragent",
-                   "Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:109.0) Gecko/20100101 Firefox/115.0"),
+        ConfigItem("Network", "useragent", "Mozilla/5.0"),
         ConfigItem("Network", "useRobots", True),
         ConfigItem("Network", "timeout", 60),
         ConfigItem("Network", "retry", 3),

PixivUtil2.py

@@ -1724,15 +1724,11 @@ def main():
               Fore.CYAN + Style.BRIGHT + "https://github.com/Nandaka/PixivUtil2?tab=readme-ov-file#a-usage" + Style.RESET_ALL)
 
         username = __config__.username
-        # if username == '':
-        #     username = input('Username ? ').rstrip("\r")
-        # else:
-        #     msg = f'Using Username: {username}'
-        #     PixivHelper.print_and_log('info', msg)
-
         password = __config__.password
-        # if password == '':
-        #     password = getpass.getpass('Password ? ')
+        if not username or not password:
+            print(Fore.RED + Style.BRIGHT + "No username and/or password found in config.ini" + Style.RESET_ALL)
+            print(Fore.YELLOW + Style.BRIGHT + "See " + Style.RESET_ALL + Fore.CYAN + Style.BRIGHT +
+                  "https://github.com/Nandaka/PixivUtil2?tab=readme-ov-file#authentication" + Style.RESET_ALL)
 
         if np_is_valid and options.number_of_pages != 0:  # Yavos: overwrite config-data
             PixivHelper.print_and_log("info", f'Limit up to: {options.number_of_pages} page(s). (set via commandline)')