debuginfod-client.c: Download section even if cached executable didn't contain it.

debuginfod-client.c: Download section even if cached executable didn't contain it.

Before attempting to download a section, cache_find_section tries to
extract the section from existing files in the cache. If it's determined
that the section must not exist, cache_find_section returns -ENOENT to
indicate that the download should be skipped.

This patch fixes a bug where cache_find_section returns -ENOENT even
though the section exists.  If the cache contains the executable but
not the debuginfo with the given build-id and the section only exists
in the debuginfo (such as any of the .debug_* sections), then
debuginfod_find_section returns -ENOENT even if the section could be
downloaded.

Fix this by having cache_find_section not return -ENOENT unless cached
debuginfo was able to be read.

Signed-off-by: Aaron Merey <amerey@redhat.com>