baseinfo: don't abort when calling g_base_info_get_name() on a GITypeInfo. Fixes #96

GITypeInfo is a GIBaseInfo so calling g_base_info_get_name() on it should do something
sensible.

g_base_info_get_name() has always been documented to return NULL in case no name
is available so return that instead.

gibaseinfo.c

@@ -377,6 +377,7 @@ g_base_info_get_name (GIBaseInfo *info)
       }
       break;
     case GI_INFO_TYPE_TYPE:
+      return NULL;
     default: ;
       g_assert_not_reached ();
       /* unnamed */