git-gui: do not end the commit message with an empty line

The commit message is processed to remove unnecessary empty lines.
In particular, it is ensured that the text ends with at most one LF
character. This one is always present, because the Tk text widget
ensures that is present.

However, did not consider that the processed text is written to the
commit message file using `puts`, which also appends a LF character,
so that the final commit message ends with two LF. Trim all trailing
LF characters, and while we are here, use `string trim`, which lets
us remove the leading LF in the same command.

Reported-by: Gareth Fenn <garethfenn@gmail.com>
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@gmx.de>
Signed-off-by: Johannes Sixt <j6t@kdbg.org>

lib/commit.tcl

@@ -214,12 +214,10 @@ You must stage at least 1 file before you can commit.
 	global comment_string
 	set cmt_rx [strcat {(^|\n)} [regsub -all {\W} $comment_string {\\&}] {[^\n]*}]
 	regsub -all $cmt_rx $msg {\1} msg
-	# Strip leading empty lines
-	regsub {^\n*} $msg {} msg
+	# Strip leading and trailing empty lines (puts adds one \n)
+	set msg [string trim $msg \n]
 	# Compress consecutive empty lines
 	regsub -all {\n{3,}} $msg "\n\n" msg
-	# Strip trailing empty line
-	regsub {\n\n$} $msg "\n" msg
 	if {$msg eq {}} {
 		error_popup [mc "Please supply a commit message.