Improve, refactor and clean up pngtest.c
Improve:
The pngtest program used to be rather relaxed upon seeing invalid
parameters in callbacks: it either ignored them, or it bailed out
of the callbacks, essentially sweeping the bug under the rug.
But no more. Now it terminates with a severe `png_error`, in which
it says what's broken and where.
Improve:
`PNG_DEBUG`, defined externally at build time, and defaulting to zero,
was assumed to be non-negative. Now it's checked.
Clean up:
In a very distant past, the pngtest program used to "travel" across
libpng versions, on its own, not necessarily accompanied by the actual
library version that it was meant to test. However, this stopped being
the case, and now is as good a time as any to remove the compatibility
workarounds that had made the aforementioned "travel" possible.
Other chores include:
* The refactoring of the user-defined chunk handling routines;
* The cleanup of an unnecessary use of volatile;
* The various cosmetic improvements of code and comments.
1 file changed
