when loading a specially crafted PSD.
After fixing the issue in the previous commit, using the poc from that
issue, a new issue surfaced where the ptr_array used for
img_a->alpha_name did not contain any names. Trying to access the
first index then caused a crash, because apparently that is only
valid if at least one item has been added.
Let's fix this by only creating the ptr_array when we know for sure
that we are going to add an item.
02886e626d