Land rapid7#7713, scriptkittie fix for SessionLogging

lands a fix for loggers not handling a nil message
Fix for rapid7#7687

Author: David Maloney

lib/rex/logging/sinks/timestamp_flatfile.rb

@@ -12,6 +12,7 @@ module Sinks
 class TimestampFlatfile < Flatfile
 
   def log(sev, src, level, msg, from) # :nodoc:
+    return unless msg.present?
     msg = msg.chop.gsub(/\x1b\[[0-9;]*[mG]/,'').gsub(/[\x01-\x02]/, " ")
     fd.write("[#{get_current_timestamp}] #{msg}\n")
     fd.flush

lib/rex/ui/text/shell.rb

@@ -272,6 +272,7 @@ def update_prompt(prompt = nil, new_prompt_char = nil, mode = false)
   #
   def print_error(msg='')
     return if (output.nil?)
+    return if (msg.nil?)
 
     self.on_print_proc.call(msg) if self.on_print_proc
     # Errors are not subject to disabled output