smb1: Prevent accessing uninitialized referenced_tree

The added pcap was created from an OSS Fuzz test case and is borderline
valid SMB traffic, but it triggered a scripting error.

Closes #2726

testing/btest/scripts/base/protocols/smb/smb1-OSS-fuzz-54883.test

@@ -0,0 +1,10 @@
+#@TEST-EXEC: zeek -b -C -r $TRACES/smb/smb1-OSS-fuzz-54883.pcap %INPUT
+#@TEST-EXEC: btest-diff weird.log
+#@TEST-EXEC: ! test -f reporter.log
+
+@load base/protocols/smb
+@load base/frameworks/notice/weird
+
+# The traffic generated by OSS Fuzz is broken to the extreme, ensure
+# the analyzer isn't disabled so the original scripting issue triggers.
+redef DPD::ignore_violations += { Analyzer::ANALYZER_SMB };