gitk: fix the context menu not appearing in the presence of submodule diffs

Currently, submodule diffs can cause the diff context menu to fail
to appear because of a couple bugs in parseblobdiffline:

* it appends the submodule name to ctext_file_lines instead of
  a line number, which breaks the binary search in find_ctext_fileinfo;

* it can desynchronize ctext_file_names and ctext_file_lines
  by appending to the former but not the latter, which also breaks
  find_ctext_fileinfo.

Fix both of these.

Note: a side effect of this patch is that the context menu also
starts appearing when you right-click on submodule diffs (and not just
regular diffs). The menu is non-functional in this case, though,
since you can't run blame on submodules.

Signed-off-by: Роман Донченко <[email protected]>
Signed-off-by: Paul Mackerras <[email protected]>

Author: SpecLad

gitk

@@ -8231,10 +8231,10 @@ proc parseblobdiffline {ids line} {
 	if {$currdiffsubmod != $fname} {
 	    $ctext insert end "\n";     # Add newline after commit message
 	}
-	set curdiffstart [$ctext index "end - 1c"]
-	lappend ctext_file_names ""
 	if {$currdiffsubmod != $fname} {
-	    lappend ctext_file_lines $fname
+	    set curdiffstart [$ctext index "end - 1c"]
+	    lappend ctext_file_names ""
+	    lappend ctext_file_lines [lindex [split $curdiffstart "."] 0]
 	    makediffhdr $fname $ids
 	    set currdiffsubmod $fname
 	    $ctext insert end "\n$line\n" filesep