Fix log browsing.
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.

Change-Id: I3fec5b88cd6a59f93a2394b94e10e8b80c61e88f
Reviewed-on: http://review.couchbase.org/9482
Tested-by: Aliaksey Artamonau <3c875bcfb3adf2a65b2ae7686ca921e6c9433147@gmail.com>
Reviewed-by: Aliaksey Kandratsenka <340b8e09ca65cd3fc686427fcfed17e87eaf61e2@gmail.com>

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