Don't allocate less memory than required

When switching from a simple to a sparse array,
keep the previously allocated size, to not corrupt
memory.

Change-Id: I33f0fb049a2ad6f24ee3703f2c333855830fe9d2
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>
Get rid of !this and similar constructs

The C++ standard doesn't allow calling member functions
on a mull object. Fix all such places, by moving the checks
to the caller where required.

Change-Id: I10fb22acaf0324d8ffd3a6d8e19152e5d32f56bb
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>