GString: Bump minimum size

GString starts out at a size of 2, which is just
not useful. Bump the minimum size to 64 to cut
down on the number of tiny reallocations we do.

glib/gstring.c

@@ -123,7 +123,7 @@ g_string_sized_new (gsize dfl_size)
   string->len   = 0;
   string->str   = NULL;
 
-  g_string_maybe_expand (string, MAX (dfl_size, 2));
+  g_string_maybe_expand (string, MAX (dfl_size, 64));
   string->str[0] = 0;
 
   return string;