gitk: Fix file list context menu for merge commits
gitk: Fix file list context menu for merge commits

Currently it displays an ugly error box, because the treediffs array
is not filled for such commits.  This fixes it by making
getmergediffline add the filenames it sees to the treediffs array
like gettreediffline does.

Signed-off-by: Alexander Gavrilov <75c96f70141fec65a655d202cd4821a09cb99fd1@gmail.com>
Signed-off-by: Paul Mackerras <19a0ba370c443ba08d20b5061586430ab449ee8c@samba.org>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git