Improved allocation of plane cells

[mulle-nat]

• size_t overflow check for cell array
• use calloc to gain mucho speed for huge dimensions

[mulle-nat]

Your last commit IMO has an error, in that it now doesn't check for cols == 0 || rows == 0 anymore, which it used to do. This is also done by my patch.

I tested it with this test code:

  for( unsigned int y = (unsigned int) -1; y != 2; y++)
    for( unsigned int x = (unsigned int) -1; x != 2; x++)
    {
      ncplane_options nopts = {
       .y = 0,
       .x = 0,
       .rows = y,
       .cols = x,
       .flags = 0
      };

      struct ncplane* test = ncplane_create(n, &nopts);
      if( test != NULL)
      {
        if( x != 1 && y != 1)
            abort();
        ncplane_destroy( test);
      }
    }

[dankamongmen]

Your last commit IMO has an error, in that it now doesn't check for cols == 0 || rows == 0 anymore, which it used to do.

wow, it sure does, doesn't it? embarrassing! thanks a lot for the catch.

[dankamongmen]

your fix for the zero check is obviously correct and necessary. i find the rest questionable.