[llvm-objcopy] - Emit error and don't crash if program header reaches past end of file.

This is https://bugs.llvm.org/show_bug.cgi?id=42122.

If an object file has a size less than program header's file [offset + size]
(i.e. if we have overflow), llvm-objcopy crashes instead of reporting a
error.

The patch fixes this issue.

Differential revision: https://reviews.llvm.org/D62898

llvm-svn: 362778