Pull request #174: problem is malloc

Fix bug in pull request #170

Squashed commit of the following:

commit d9b46cf6f7de2088187f48722de2313d1d0d32ca
Author: van Andel, Gerhard <gvanande@ball.com>
Date:   Tue Aug 24 17:39:50 2021 -0600

    problem is malloc

cosmos/ext/cosmos/ext/structure/structure.c

@@ -520,7 +520,7 @@ static VALUE binary_accessor_read(VALUE self, VALUE param_bit_offset, VALUE para
     {
       string_length = upper_bound - lower_bound + 1;
       string = malloc(string_length + 1);
-      if (unsigned_char_array == NULL) {
+      if (string == NULL) {
         rb_raise(rb_eNoMemError, "malloc of %d returned NULL", string_length + 1);
       }
       memcpy(string, buffer + lower_bound, string_length);