replace base64 regex string (#1919)

* replace base64 regex string

* replace base64RegExp String due to app crash in release mode, throws stack overflow error

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Co-authored-by: SalmanAhmed <salman.ahmed@digicopsolutions.com>

flutter_quill_extensions/lib/utils/patterns.dart

@@ -1,5 +1,5 @@
 RegExp base64RegExp = RegExp(
-  r'^(?:[A-Za-z0-9+\/]{4})*(?:[A-Za-z0-9+\/]{2}==|[A-Za-z0-9+\/]{3}=|[A-Za-z0-9+\/]{4})$',
+  r'^(?:[A-Za-z0-9+\/][A-Za-z0-9+\/][A-Za-z0-9+\/][A-Za-z0-9+\/])*(?:[A-Za-z0-9+\/]{2}==|[A-Za-z0-9+\/]{3}=|[A-Za-z0-9+\/]{4})$',
 );
 
 final imageRegExp = RegExp(