[recipes/unit_convert_test: 9/10] Fix a compiler warning

[Matthias Clasen <matthiasc src gnome org>]

commit 6679528df2aac5fdd27c1c1a6ed6d34505c85041
Author: Matthias Clasen <mclasen redhat com>
Date:   Wed Jul 12 18:26:02 2017 -0400

    Fix a compiler warning

 src/gr-unit.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/src/gr-unit.c b/src/gr-unit.c
index cf1a156..d62bec3 100644
--- a/src/gr-unit.c
+++ b/src/gr-unit.c
@@ -109,7 +109,7 @@ gr_unit_get_id_number (const char *name)
         GrUnit *unit = find_unit (name);
         if (unit)
                 return unit->id_number;
-        return NULL;
+        return 0;
 }
 
 const char *