gitk: sanitize 'open' arguments: revisit recently updated 'open' calls

gitk: sanitize 'open' arguments: revisit recently updated 'open' calls

The previous commits bb5cb23daf75 (gitk: prevent overly long command
lines, 2023-01-24) rewrote a set of the 'open' calls substantially.
These were then later updated by 7dd272eca153 (gitk: escape file paths
before piping to git log, 2023-01-24) and d5d1b91e5327 (gitk: encode
arguments correctly with "open", 2025-03-07). In the preceding merge,
the conversions to a safe_open variant were undone to ensure that the
principal operation of the new 'open' calls is not modified by accident.

Since the 'open' calls now pass a redirection from a Tcl string as
stdin, convert the calls to 'safe_open_command_redirect'.

Signed-off-by: Johannes Sixt <j6t@kdbg.org>
Signed-off-by: Taylor Blau <me@ttaylorr.com>