[gdb] Don't init history in batch mode

I noticed in captured_main_1 that init_history is called just before bailing
out if batch_flag is true.

The history is used only in an interactive session, so there's no need to
initialize it in batch mode.

Fix this by moving init_history to after the batch mode check.

Tested on x86_64-linux.

Approved-By: Andrew Burgess <aburgess@redhat.com>