logextract: Fix handling of messages with retransmits

Properly handle the case where the original sequence number of a
message is not known.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

scripts/logextract.py

@@ -103,6 +103,7 @@ class GatherShutdown:
         ext_clock = add_high_bits(clock, exp_clock, 0xffffffff)
         return sample_time + (ext_clock - sample_clock) / freq
     def annotate(self, line, seq, ts):
+        if seq is not None:
             line = repl_seq_r.sub(r"\g<0>(%d)" % (seq,), line)
         def clock_update(m):
             return m.group(0)[:-1] + "(%.6f) " % (