Fix: Added fallback decoding for Base64 encoded strings

[Chvalov]

I encountered an issue where the importWStalker method in the LoggerImport class fails to decode certain Base64 encoded strings due to illegal characters. The error stack trace indicates an IllegalArgumentException is thrown when trying to decode these strings.

java.lang.IllegalArgumentException: Illegal base64 character 2f
	at java.base/java.util.Base64$Decoder.decode0(Base64.java:852)
	at java.base/java.util.Base64$Decoder.decode(Base64.java:570)
	at burp.Ztmx.decode(Unknown Source)
	at burp.Ztmx.decode(Unknown Source)
	at 

To fix this issue, I implemented a two-step decoding process:
First, attempt to decode using standard Base64.
If standard Base64 decoding fails, catch the IllegalArgumentException and attempt to decode using URL-safe Base64.
This approach ensures that both standard and URL-safe Base64 encoded strings are correctly processed.

This change addresses the issue where some Base64 encoded strings were causing decoding failures due to illegal characters.

[Chvalov]

This fix was already provided earlier 19aefdf, it's strange that the current version contains the problematic code 🤔