"Edit" function in tree and diff view opens the wrong path under certain conditions in submodules

[h3xx]

Part One

When the git repo you're viewing is cloned as a submodule, e opens the wrong file path for editing, but only if your working directory isn't the top directory of the submodule if that makes any sense.

Steps to reproduce:

1. Run these shell lines:

   $ mkdir temp ; cd temp
   $ git init
   $ git submodule add https://github.com/jonas/tig.git
   $ cd tig/src
   $ tig

2. Then in the resulting tig window, press enter on a commit, then use j/k to highlight a diff-stat line and press e. It will give the error "Failed to open file: ..."

Expected behavior: Open the file in $EDITOR from the highlighted line in the diff view.

Part Two

Likewise, pressing e on a file when in tree view results in the editor opening a non-existent file, but only sometimes. It seems to have to do with it being both a submodule, and trying to open a file using tree view two levels above the directory where you started tig.

Steps to reproduce, part 2:

$ mkdir temp ; cd temp
$ git init
$ git submodule add https://github.com/jonas/tig.git
$ cd tig/tests/graph
$ tig

2. Press t to enter tree view, then press enter on .. twice, so you're at the top level for the submodule.
3. Highlight a file in that directory like INSTALL.adoc and press e.

I find it will open temp/INSTALL.adoc which doesn't exist, instead of temp/tig/INSTALL.adoc.

Tested under 58aa1d4 running on Slackware Linux x86_64 with git-2.16.1.

[h3xx]

See f99d2af for a test that proves it's an issue.

[h3xx]

Confirmed fixed. Thanks!

[jonas]

Thanks for testing.