libipt, section: fix address overflow bug

For very big addresses, the region to read might overflow and end up before
the section's memory region.  This case has not been handled causing us to
access random memory and crashing the library.

Check for such overflows.

Change-Id: Ia25e3216501e6416d294351b6082684eba788b92
Signed-off-by: Markus Metzger <markus.t.metzger@intel.com>