Log Message:
Changes 0.55.0:

core:
* Fix abort in files with broken Decode arrays.
* Fix memory leak (and probably logic bug) parsing broken XRef entries.
* Fix memory leak when reconstructing broken files.
* Minor optimization
* Fix regression in GfxIndexedColorSpace::mapColorToBase.
* Fix memory leak in error condition

cpp:
* Return nullptr if the page at index can't be fetched.

build system:
* Fail by default if libjpeg is not available
* Fail by default if libopenjpeg2/1 is not available