line-log: fix crash when combined with pickaxe options

line-log: fix crash when combined with pickaxe options

queue_diffs() passes the caller's diff_options, which may carry
user-specified pickaxe state, to diff_tree_oid() and diffcore_std()
when detecting renames for line-level history tracking.  When pickaxe
options are present on the command line (-G and -S to filter by text
pattern, --find-object to filter by object identity), diffcore_std()
also runs diffcore_pickaxe(), which may discard diff pairs that are
relevant for rename detection.  Losing those pairs breaks rename
following.

Before a2bb801f6a (line-log: avoid unnecessary full tree diffs,
2019-08-21), this silently truncated history at rename boundaries.
That commit moved filter_diffs_for_paths() inside the rename-
detection block, so it only runs when diff_might_be_rename() returns
true.  When pickaxe discards a rename pair, the rename goes
undetected, and a deletion pair at a subsequent commit passes
through uncleaned, reaching process_diff_filepair() with an invalid
filespec and triggering an assertion failure.

Fix this by building a private diff_options for the rename-detection
path inside queue_diffs(), following the same pattern used by blame's
find_rename().  This isolates the rename machinery from unrelated
user-specified options.

Reported-by: Matthew Hughes <matthewhughes934@gmail.com>
Signed-off-by: Michael Montalbo <mmontalbo@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>