[libgit2-glib] ggit-branch-enumerator.c: Check for NULL enumerator in ggit_branch_enumerator_ref

[Igor Gnatenko <ignatenko src gnome org>]

commit a74811f28260f7d05e9bda74889b7f5c681bd1a4
Author: Brian C. Lane <bcl redhat com>
Date:   Wed Aug 30 11:22:22 2017 -0700

    ggit-branch-enumerator.c: Check for NULL enumerator in ggit_branch_enumerator_ref
    
    And adjust return annotation.

 libgit2-glib/ggit-branch-enumerator.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)
---
diff --git a/libgit2-glib/ggit-branch-enumerator.c b/libgit2-glib/ggit-branch-enumerator.c
index 1b87dc0..b127f53 100644
--- a/libgit2-glib/ggit-branch-enumerator.c
+++ b/libgit2-glib/ggit-branch-enumerator.c
@@ -32,6 +32,8 @@ _ggit_branch_enumerator_wrap (git_branch_iterator *iter)
 GgitBranchEnumerator *
 ggit_branch_enumerator_ref (GgitBranchEnumerator *enumerator)
 {
+       g_return_val_if_fail (enumerator != NULL, NULL);
+
        g_atomic_int_inc (&enumerator->ref_count);
        return enumerator;
 }