Development/scripts: Update stack tool

The tool was broken for ASAN traces. Add a missing key to the
dictionary.

Bug: 24133462
Change-Id: I6e5b60441c9c602cd1381c1cb32947a1425c7069
diff --git a/scripts/stack_core.py b/scripts/stack_core.py
index 69c4e1f..963f7d5 100755
--- a/scripts/stack_core.py
+++ b/scripts/stack_core.py
@@ -195,6 +195,7 @@
       match = self.sanitizer_trace_line.match(line)
       return {"frame": match.group("frame"),
               "offset": match.group("offset"),
+              "so_offset": None,
               "dso": match.group("dso"),
               "symbol_present": False,
               "symbol_name": None}