rc tools git: fix initial position of blame of deleted line

When running git blame in a "git show" buffer, we annotate the youngest
version of the file that has the line referenced by the diff line
at cursor.
In case the cursor is on an added or context line, we simply show
the version from the surrounding commit.

When the cursor is on a deleted line, we show the parent commit,
which still has the deleted line.  However there is a bug: we use
the line number in the new version of the file. Fix that.

rc/tools/git.kak

@@ -225,9 +225,14 @@ define-command -params 1.. \
                         require-module diff
                         try %{
                             diff-parse END %{
-                                $commit = "$commit~" if $diff_line_text =~ m{^[-]};
+                                my $line = $file_line;
+                                if ($diff_line_text =~ m{^[-]}) {
+                                    $commit = "$commit~";
+                                    $line = $other_file_line;
+                                }
+                                $line = $line or 1;
                                 printf "echo -to-file '${kak_response_fifo}' -quoting shell %s %s %d %d",
-                                    $commit, quote($file), ($file_line or 1), ('${kak_cursor_column}' - 1);
+                                    $commit, quote($file), $line, ('${kak_cursor_column}' - 1);
                             }
                         } catch %{
                             echo -to-file '${kak_response_fifo}' -quoting shell -- %val{error}

test/tools/git/blame-in-diff/cmd

@@ -0,0 +1 @@
+:run<ret>

test/tools/git/blame-in-diff/enabled

@@ -0,0 +1,2 @@
+#!/bin/sh
+command -v git >/dev/null

test/tools/git/blame-in-diff/env

@@ -0,0 +1 @@
+../env

test/tools/git/blame-in-diff/in

@@ -0,0 +1,3 @@
+line 1
+line 2
+line 3

test/tools/git/blame-in-diff/kak_selection

@@ -0,0 +1,2 @@
+line 2
+

test/tools/git/blame-in-diff/rc

@@ -0,0 +1,14 @@
+declare-option str jumpclient
+source "%val{runtime}/rc/filetype/diff.kak"
+source "%val{runtime}/rc/tools/git.kak"
+
+define-command run %{
+    git init
+    git add
+    git commit --message 'initial commit'
+    execute-keys %{2gIchanged <esc>}
+    write
+    git commit --all --message 'changed line 2'
+    # Show the commit, jumping to the new version of line 2.
+    git blame-jump
+}

test/tools/git/blame-in-diff/script

@@ -0,0 +1,11 @@
+ui_out -ignore 7
+ui_out -ignore 11
+
+# We've jumped to the new version of line 2. Move to the old version so we
+# can annotate the old file.
+ui_in '{ "jsonrpc": "2.0", "method": "keys", "params": [ "k:git blame<ret>" ] }'
+ui_out -ignore 11
+
+# We should have jumped to the old version of line 2, assert on kak_selection.
+ui_in '{ "jsonrpc": "2.0", "method": "keys", "params": [ "x" ] }'
+ui_out -ignore 5