fix overflow in allocation size calculation in apreq_param_make

[jmestwa-coder]

Summary

Fix integer overflow in apreq_param_make() when computing the allocation size.

Root Cause

The allocation size was calculated using unchecked arithmetic:

nlen + vlen + 1 + sizeof(*param)

For sufficiently large values, this addition can overflow apr_size_t, leading to an incorrect (wrapped) allocation size.

Fix

Add bounds checks before performing the allocation:

• Ensure nlen + vlen does not overflow
• Ensure the final size including structure and terminator fits in apr_size_t
• Use the validated size for allocation

Behavior

• Valid inputs: unchanged
• Overflow cases: function returns NULL (already handled by callers)

Impact

Ensures allocation size calculations are safe and do not rely on implicit assumptions about input sizes.