Avoid uninitialized variable error.

src/revparse.c

@@ -506,8 +506,8 @@ static int handle_linear_syntax(git_object **out, git_object *obj, const char *m
    /* "~" is the same as "~1" */
    if (*movement == '\0') {
       n = 1;
-   } else {
-      git__strtol32(&n, movement, NULL, 0);
+   } else if (git__strtol32(&n, movement, NULL, 0) < 0) {
+      return GIT_ERROR;
    }
    commit1 = (git_commit*)obj;
 

tests-clar/refs/revparse.c

@@ -104,6 +104,9 @@ void test_refs_revparse__to_type(void)
 
 void test_refs_revparse__linear_history(void)
 {
+   cl_git_fail(git_revparse_single(&g_obj, g_repo, "foo~bar"));
+   cl_git_fail(git_revparse_single(&g_obj, g_repo, "master~bar"));
+
    test_object("master~0", "a65fedf39aefe402d3bb6e24df4d4f5fe4547750");
    test_object("master~1", "be3563ae3f795b2b4353bcce3a527ad0a4f7f644");
    test_object("master~2", "9fd738e8f7967c078dceed8190330fc8648ee56a");