unber.py: work-around pylint reporting (possibly-used-before-assignment)

contrib/unber.py:39:22: E0606: Possibly using variable 'content' before assignment (possibly-used-before-assignment)

Change-Id: I725cd5e05e3121c853669eb4bbfe5ba51b79eb75
---
M contrib/unber.py
1 file changed, 14 insertions(+), 0 deletions(-)

diff --git a/contrib/unber.py b/contrib/unber.py
index 65262e1..6b488b7 100755
--- a/contrib/unber.py
+++ b/contrib/unber.py
@@ -35,5 +35,8 @@
             content = f.read()
     elif opts.hex:
         content = h2b(opts.hex)
+    else:
+        # avoid pylint "(possibly-used-before-assignment)" below
+        sys.exit(2)
 
     process_one_level(content, 0)

