dwarf-reader: handle binaries with missing symtab

dwarf-reader: handle binaries with missing symtab

A broken elf file might not have a valid symtab. As of now we would hit
an ABG_ASSERT and crash. Let's catch that case and bail out instead.

        * src/abg-dwarf-reader.cc (load_symbol_maps_from_symtab_section):
        Handle elf file with missing symtab.
        * tests/test-read-dwarf.cc (InOutSpec): add test case.
        * tests/data/test-read-dwarf/test26-bogus-binary.elf: new test data.

Signed-off-by: Matthias Maennich <maennich@google.com>