garray: Just use one bit to hold the null teminated state

This is probably ignored for saving space because of padding optimizations,
but since we want this value to be either 0 or 1, this enforces this too.

glib/garray.c

@@ -1072,7 +1072,7 @@ struct _GRealPtrArray
   guint           len;
   guint           alloc;
   gatomicrefcount ref_count;
-  guint8          null_terminated; /* always either 0 or 1, so it can be added to array lengths */
+  guint8          null_terminated : 1; /* always either 0 or 1, so it can be added to array lengths */
   GDestroyNotify  element_free_func;
 };