dpkg-genchanges: Fix check for expected number of binary artifacts

Only count the binaries that we are going to include in the upload,
instead of guessing using implicit counts.

debian/changelog

@@ -33,6 +33,8 @@ dpkg (1.18.19) UNRELEASED; urgency=medium
   * Do not compute the architecture list twice in dpkg-genchanges.
   * Include .buildinfo files also for source-only uploads in dpkg-genchanges.
     Closes: #846164
+  * Fix check for expected number of binary artifacts in dpkg-genchanges, to
+    only take into account the artifacts that we are distributing.
   * Portability:
     - On GNU/Hurd try to use the new process executable name attribute from
       libps, to properly match on start-stop-daemon --exec.

scripts/dpkg-genchanges.pl

@@ -303,12 +303,9 @@ if (build_has_any(BUILD_SOURCE)) {
     $origsrcmsg = g_('binary-only upload (no source code included)');
 }
 
-my $dist_count = 0;
+my $dist_binaries = 0;
 
-$dist_count = $dist->load($fileslistfile) if -e $fileslistfile;
-
-error(g_('binary build with no binary artifacts found; cannot distribute'))
-    if build_has_any(BUILD_BINARY) && $dist_count == 0;
+$dist->load($fileslistfile) if -e $fileslistfile;
 
 foreach my $file ($dist->get_files()) {
     my $f = $file->{filename};
@@ -336,8 +333,12 @@ foreach my $file ($dist->get_files()) {
     }
 
     $checksums->add_from_file("$uploadfilesdir/$f", key => $f);
+    $dist_binaries++;
 }
 
+error(g_('binary build with no binary artifacts found; cannot distribute'))
+    if build_has_any(BUILD_BINARY) && $dist_binaries == 0;
+
 # Scan control info of all binary packages
 foreach my $pkg ($control->get_packages()) {
     my $p = $pkg->{'Package'};