darray: check integer overflow

darray: check integer overflow

In commit b9b3593cbdeb7f5b02d50cecaba6a0b47d4979ad,
darray is changed to use unsigned int instead of size_t
to reduce memory usage.
However, an integer overflow may occur due to arithmetic operation
(addition) between values.

To address this issue, this commit adds checks if this sums don't
exceed their type's maximum value.

Change-Id: Iaa689bb3beff0f991c8b9b6d8fc541f971d8c735