Bug 6679 - [SIGNED-OFF] fix 7 perlcritic violations in C4/Biblio.pm

Bug 6679 - [SIGNED-OFF] fix 7 perlcritic violations in C4/Biblio.pm

- Expression form of "eval" at line 492, column 12.  See page 161 of PBP.  (Severity: 5)

- "return" statement with explicit "undef" at line 891, column 5.  See page 199 of PBP.  (Severity: 5)

- Subroutine prototypes used at line 1148, column 1.  See page 194 of PBP.  (Severity: 5)

Signed-off-by: Jonathan Druart <jonathan.druart@biblibre.com>
Signed-off-by: Paul Poulain <paul.poulain@biblibre.com>