gitk: don't highlight files after submodules as submodules

gitk applies submodule highlighting (coloring lines starting with
"  >" and "  <") when `currdiffsubmod` is not an empty string.
However, it fails to reset `currdiffsubmod` after a submodule diff
ends, so any file diffs following a submodule diff will still be
highlighted as if they were submodule diffs.

There are two problems with the way gitk tries to reset `currdiffsubmod`:

1. The code says `set $currdiffsubmod` instead of `set currdiffsubmod`,
   so it actually sets the variable whose name is the submodule path
   instead.

2. It tries to do it after the first line in a submodule diff, which
   is incorrect, since submodule diffs can contain multiple lines.

Fix this by resetting `currdiffsubmod` when a file diff starts.

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

Author: SpecLad

gitk

@@ -8150,6 +8150,8 @@ proc parseblobdiffline {ids line} {
 	}
 	# start of a new file
 	set diffinhdr 1
+	set currdiffsubmod ""
+
 	$ctext insert end "\n"
 	set curdiffstart [$ctext index "end - 1c"]
 	lappend ctext_file_names ""
@@ -8233,11 +8235,9 @@ proc parseblobdiffline {ids line} {
 	    $ctext insert end "$line\n" filesep
 	}
     } elseif {$currdiffsubmod != "" && ![string compare -length 3 "  >" $line]} {
-	set $currdiffsubmod ""
 	set line [encoding convertfrom $diffencoding $line]
 	$ctext insert end "$line\n" dresult
     } elseif {$currdiffsubmod != "" && ![string compare -length 3 "  <" $line]} {
-	set $currdiffsubmod ""
 	set line [encoding convertfrom $diffencoding $line]
 	$ctext insert end "$line\n" d0
     } elseif {$diffinhdr} {