Unlikely-to-happen crash in ecpg driver caused by NULL-pointer check not done

Hi all,

In ecpg_add_mem of memory.c, we use ecpg_alloc but there is actually
no NULL-pointer check. If an OOM shows up exactly at this point, this
is likely to cause a crash. Attached patch adds some extra processing
to ecpg_add_mem to check if the allocation fails, and to fail properly
if an OOM appears.
This issue has been pointed out by Coverity, and I guessed the legwork
needed by myself.
Regards,
--
Michael