gitweb: Fix 'history' view for deleted files with history

gitweb: Fix 'history' view for deleted files with history

When asked for history of a file which is not present in given branch
("HEAD", i.e. current branch, or given by transient $hash_hase ('hb')
parameter), but is present deeper in the history (meaning that "git
rev-list --full-history $hash_base -- $file_name" is not empty), and
there is no $hash ('h') parameter set for a file, gitweb would spew
multiple of "Use of uninitialized value" warnings, and some links
would be missing.  This commit fixes this bug.

This bug occurs in the rare cases when "git log -- <path>" is empty
and "git log --full-history -- <path>" is not, or to be more exact in
the cases when full-history starts later than given branch.  It can
happen if you are using handcrafted gitwb URL, or if you follow
generic 'history' link or bookmark for a file which got deleted.

Gitweb tried to get file type ('tree', or 'blob', or even 'commit')
from the commit we start searching from (where the file was not
present), and not among found commits.  This was the cause of "Use of
uninitialized value" warnings.

This commit also add tests for such situation to t9500 test.

While we are it, return HTTP error if there is _no_ history; it means
that file or directory was not found (for given branch).  Also error
out if type of item could not be found: it should not happen now, but
better be sure.

Signed-off-by: Jakub Narebski <jnareb@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>