[bp] Fix log browsing.
[bp] Fix log browsing.

When number of used log files has not yet reached the maximum
(i.e. there was no wrap around) then current file index returned by
read_index_file is greater than the reported number of files by
one. Tackle this correctly.

Originally reviewed on http://review.couchbase.org/9482

Change-Id: Id9d02293b3eb6579138e410661c878dee96dddd2
Reviewed-on: http://review.couchbase.org/13541
Reviewed-by: Aliaksey Artamonau <3c875bcfb3adf2a65b2ae7686ca921e6c9433147@gmail.com>
Reviewed-by: Aliaksey Kandratsenka <340b8e09ca65cd3fc686427fcfed17e87eaf61e2@gmail.com>
Tested-by: Aliaksey Kandratsenka <340b8e09ca65cd3fc686427fcfed17e87eaf61e2@gmail.com>

nimishzynga/ns_server,vzasade/ns_server,nimishzynga/ns_server,mschoch/ns_server,vzasade/ns_server,t3rm1n4l/ns_server,nimishzynga/ns_server,mschoch/ns_server,daverigby/ns_server,membase/ns_server,ceejatec/ns_server,mschoch/ns_server,membase/ns_server,mschoch/ns_server,daverigby/ns_server,vzasade/ns_server,daverigby/ns_server,daverigby/ns_server,ceejatec/ns_server,membase/ns_server,vzasade/ns_server,membase/ns_server,pavel-blagodov/ns_server,t3rm1n4l/ns_server,t3rm1n4l/ns_server,nimishzynga/ns_server,nimishzynga/ns_server,mschoch/ns_server,ceejatec/ns_server,ceejatec/ns_server,mschoch/ns_server,membase/ns_server,pavel-blagodov/ns_server,pavel-blagodov/ns_server,nimishzynga/ns_server,t3rm1n4l/ns_server,pavel-blagodov/ns_server,membase/ns_server,daverigby/ns_server,ceejatec/ns_server,ceejatec/ns_server,t3rm1n4l/ns_server