[evince] build: fix meson build when ps and dvi are disabled

[Germán Poo-Caamaño <gpoo src gnome org>]

commit 0157194be5f45fdaf4ffeaba605403fcedb93449
Author: Jason Crain <jcrain src gnome org>
Date:   Tue Sep 25 15:28:46 2018 -0600

    build: fix meson build when ps and dvi are disabled
    
    When building with both ps and dvi support disabled, meson fails with
    the message `Unknown variable "libspectre_dep"`. This is because
    libspectre_dep is set in a conditional statement. Fix it by setting
    libspectre_dep to a disabler object when ps and dvi support are
    disabled.

 meson.build | 2 ++
 1 file changed, 2 insertions(+)
---
diff --git a/meson.build b/meson.build
index ed02dbdd..26b910af 100644
--- a/meson.build
+++ b/meson.build
@@ -315,6 +315,8 @@ if not get_option('ps').disabled() or not get_option('dvi').disabled()
   libspectre_req_version = '>= 0.2.0'
   libspectre_dep = dependency('libspectre', version: libspectre_req_version, required: false)
   config_h.set('HAVE_SPECTRE', libspectre_dep.found())
+else
+  libspectre_dep = disabler()
 endif
 
 # *** Comic Book ***