Use array bounds for optional variable bounds checks

[gold2718]

In order for bounds checking of optional array variables to succeed, the check should use the array's real lower and upper bounds instead of 1 and the array's size.

User interface changes?: No

Fixes: #651

Testing:
test removed:
unit tests:
system tests: PASS
manual testing: Check for proper code generation

[climbfuji]

Do we have a test for this? This all looks good but would be nice to see it in action :-)

[dustinswales]

@gold2718 I'm confused by these changes. #651 is not related to optional variables.

[gold2718]

@gold2718 I'm confused by these changes. #651 is not related to optional variables.

Also, it does not work properly.