Add a subtract test found by afl
diff --git a/tests/subtract.txt b/tests/subtract.txt
index 4d7852e..dbc46be 100644
--- a/tests/subtract.txt
+++ b/tests/subtract.txt
@@ -29,3 +29,4 @@
 979519669 - 3018100865
 929002449 - 3280677283
 0 - -525898
+3- - -3
diff --git a/tests/subtract_results.txt b/tests/subtract_results.txt
index 8045d4a..6850b5b 100644
--- a/tests/subtract_results.txt
+++ b/tests/subtract_results.txt
@@ -33,3 +33,4 @@
 -2038581196
 -2351674834
 525898
+0