dpkg: Fix --audit to report missing and empty architecture fields

The parser always converts the value from DPKG_ARCH_NONE to
DPKG_ARCH_EMPTY, so we will handle both here to avoid any such
problem in the future.

Regression introduced in commit 0238c795df88925c6579f740c7681ade22e88625.

debian/changelog

@@ -70,6 +70,8 @@ dpkg (1.18.0) UNRELEASED; urgency=low
   * Fix short-lived memory leaks in dpkg-deb and libdpkg. Closes: #769515
   * Fix «dpkg-deb -b» filename generation when the package does not contain
     an Architecture field. Regression introduced in dpkg 1.16.2.
+  * Fix «dpkg --audit» to report missing and empty architecture fields.
+    Regression introduced in dpkg 1.16.2.
 
   [ Updated manpages translations ]
   * German (Helge Kreutzmann).

src/enquiry.c

@@ -143,7 +143,7 @@ static const struct audit_problem audit_problems[] = {
     "database, they need to be reinstalled:\n")
   }, {
     .check = audit_arch,
-    .value.number = DPKG_ARCH_NONE,
+    .value.number = DPKG_ARCH_EMPTY,
     .explanation = N_("The following packages do not have an architecture:\n")
   }, {
     .check = audit_arch,