keep it from migrating more than once into explorer.exe

thanks for noticing egypt
we should add a migrate_explorer to the post api

Author: kernelsmith

modules/post/windows/gather/screen_spy.rb

@@ -137,9 +137,10 @@ def migrate_explorer
 				begin
 					session.core.migrate(p['pid'].to_i)
 					print_status("Migration successful")
+					return p['pid']
 				rescue
 					print_status("Migration failed.")
-					return
+					return nil
 				end
 			end
 		end