gitk: fix file name encoding in diff hunk headers

Decode file names from system encoding in all diff hunk header lines, not
just the first (i.e. print nice file names in 'rename from' / 'rename to' /
'Binary files' lines, too).

Signed-off-by: Karsten Blees <blees@dcon.de>

gitk-git/gitk

@@ -7855,6 +7855,7 @@ proc getblobdiffline {bdf ids} {
 		set diffinhdr 0
 		continue
 	    }
+	    set line [encoding convertfrom $line]
 	    $ctext insert end "$line\n" filesep
 
 	} else {