Fix incorrect handling of invalid negative object ids

Fix two errors introduced in #1110 and #1112. Since
#1110, encountering the invalid indirect reference #1110
-2147483648 n R produces an integer underflow which, if
 undetected, immediately trigger a logic error. Since
 #1112, object -1 0 R may be incorrectly identified as
 an earlier generation of itself and deleted,
 invalidating a live iterator.

1 files changed, 1 insertions, 1 deletions

diff --git a/fuzz/qtest/fuzz.test b/fuzz/qtest/fuzz.test
index adce995c..7ca371fd 100644
--- a/fuzz/qtest/fuzz.test
+++ b/fuzz/qtest/fuzz.test
@@ -20,7 +20,7 @@ my @fuzzers = (
     ['pngpredictor' => 1],
     ['runlength' => 6],
     ['tiffpredictor' => 1],
-    ['qpdf' => 54],             # increment when adding new files
+    ['qpdf' => 56],             # increment when adding new files
     );
 
 my $n_tests = 0;