libdpkg: Never return NULL from pkg_db_find_singleton()

lib/dpkg/pkg-db.c

@@ -120,6 +120,9 @@ pkg_db_find_singleton(const char *name)
 
   set = pkg_db_find_set(name);
   pkg = pkgset_get_singleton(set);
+  if (pkg == NULL)
+    ohshit(_("ambiguous package name '%s' with more "
+             "than one installed instance"), set->name);
 
   return pkg;
 }

src/enquiry.c

@@ -322,9 +322,6 @@ assert_version_support(const char *const *argv,
   modstatdb_open(msdbrw_readonly);
 
   pkg = pkg_db_find_singleton("dpkg");
-  if (pkg == NULL)
-    internerr("more than one dpkg instance installed");
-
   switch (pkg->status) {
   case stat_installed:
   case stat_triggerspending: