src/readelf.c: Access symbol and version data only if available

src/readelf.c: Access symbol and version data only if available

handle_dynamic_symtab can attempt to read symbol and version data from
file offset of 0 or address of 0 if the associated DT_ tags aren't found.

Fix this by only reading symbol and version data when non-zero file
offsets/addresses have been found.

https://sourceware.org/bugzilla/show_bug.cgi?id=32864

Suggested-by: Constantine Bytensky <cbytensky@gmail.com>
Signed-off-by: Aaron Merey <amerey@redhat.com>