versioner: fix off-by-one error in header guard calculation.
This was causing redundant guards to be emitted in cases where
declarations were already guarded by another macro.
Bug: http://b/30170081
Change-Id: I9080838fbea5a56225df4b26d0918657fb6c4f21
Test: python run_tests.py
diff --git a/tools/versioner/tests/preprocessor_idempotence/run.sh b/tools/versioner/tests/preprocessor_idempotence/run.sh
new file mode 100644
index 0000000..1b0aae2
--- /dev/null
+++ b/tools/versioner/tests/preprocessor_idempotence/run.sh
@@ -0,0 +1,4 @@
+rm -rf out
+set -e
+versioner headers -i -o out
+diff -q -w -B out expected