fix build: make check_radio_versions.py okay with no args

Change-Id: I3539383d9761b57152c04ba9198c724509ba6223
diff --git a/tools/check_radio_versions.py b/tools/check_radio_versions.py
index 83d3ab2..ebe621f 100755
--- a/tools/check_radio_versions.py
+++ b/tools/check_radio_versions.py
@@ -22,6 +22,9 @@
 except ImportError:
   from sha import sha as sha1
 
+if len(sys.argv) < 2:
+  sys.exit(0)
+
 build_info = {}
 f = open(sys.argv[1])
 for line in f: