[seahorse] Meson: fix build with disabled options.

[Niels De Graef <nielsdg src gnome org>]

commit b7bb0c34d8992e537c3cf08b8afe41485fbb010f
Author: Niels De Graef <nielsdegraef gmail com>
Date:   Tue Nov 21 19:11:31 2017 +0100

    Meson: fix build with disabled options.

 meson.build |    6 +++---
 1 files changed, 3 insertions(+), 3 deletions(-)
---
diff --git a/meson.build b/meson.build
index e6237db..52958c5 100644
--- a/meson.build
+++ b/meson.build
@@ -101,14 +101,14 @@ if check_compatible_gpg
   endif
 endif
 
-pkcs11_dep = valac.find_library('pkcs11')
+pkcs11_dep = valac.find_library('pkcs11', required: with_pkcs11)
 if with_pkcs11 and not pkcs11_dep.found()
   error('Required library "pkcs11" not found (needed for PKCS#11 support)')
 endif
 
-libldap = cc.find_library('ldap')
-liblber = cc.find_library('lber')
 if with_ldap
+  libldap = cc.find_library('ldap')
+  liblber = cc.find_library('lber')
   if not libldap.found()
     error('Required library "ldap" not found (needed for LDAP support)')
   elif not liblber.found()