git-gui: update in-memory config when changing config options

When the user updates any config variable from the options menu, the new
config gets saved, but the in-memory state of the config variables is
not updated. This results in the old settings being used until the user
either opens the options menu again (which triggers a call to
load_config), or re-starts git-gui.

This change fixes that problem by re-loading the config variables when
the Save button is pressed in the options menu.

Signed-off-by: Pratyush Yadav <me@yadavpratyush.com>

Author: prati0100

lib/option.tcl

@@ -344,6 +344,7 @@ proc do_save_config {w} {
 	if {[catch {save_config} err]} {
 		error_popup [strcat [mc "Failed to completely save options:"] "\n\n$err"]
 	}
+	load_config 1
 	reshow_diff
 	destroy $w
 }