Fix for multiple use.

[fujiwara]

Hi.

This PR ensures to apply_prof() called only once per profiler package.
When use Devel::KYTProf called multiple times, Profiler::DBI fails tests as below.

t/dbi.t ...................... 1/?
#   Failed test at t/dbi.t line 29.
#                   'Use of uninitialized value in sprintf at /Users/fujiwara/src/github.com/fujiwara/perl5-devel-kytprof/.build/oJfbj5NQ/blib/lib/Devel/KYTProf.pm line 140.
# Use of uninitialized value in sprintf at /Users/fujiwara/src/github.com/fujiwara/perl5-devel-kytprof/.build/oJfbj5NQ/blib/lib/Devel/KYTProf.pm line 140.
#     0.251 ms  [DBI::st]    (1 rows)  | main:27
# '
#     doesn't match '(?^:\[DBI::st\]  insert into mock \(id, name\) values \(\?,\?\) \(bind: 1, nekokak\) \(1 rows\)  \|)'

#   Failed test at t/dbi.t line 44.
#                   'Use of uninitialized value in sprintf at /Users/fujiwara/src/github.com/fujiwara/perl5-devel-kytprof/.build/oJfbj5NQ/blib/lib/Devel/KYTProf.pm line 140.
# Use of uninitialized value in sprintf at /Users/fujiwara/src/github.com/fujiwara/perl5-devel-kytprof/.build/oJfbj5NQ/blib/lib/Devel/KYTProf.pm line 140.
#     0.075 ms  [DBI::st]    (1 rows)  | main:42
# '
#     doesn't match '(?^:\[DBI::st\]  insert into mock \(id, name\) values \(\?,\?\) \(bind: 2, onishi\) \(1 rows\)  \|)'
# Looks like you failed 2 tests of 2.

[Songmu]

Indeed, I thought this is a needed feature.
Thank you.

[Songmu]

Released as 0.9992.