git-gui: Reorganized startup procedure to ensure gitdir is right.

Because we cd after getting the cdup value from Git we can't try
to get the gitdir until after we perform the cd, as usually the
gitdir is relative to the current working directory.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

git-gui

@@ -939,7 +939,7 @@ proc error_popup {msg} {
 }
 
 proc show_msg {w top msg} {
-	global gitdir appname
+	global gitdir appname mainfont
 
 	message $w.m -text $msg -justify left -aspect 400
 	pack $w.m -side top -fill x -padx 5 -pady 10
@@ -1465,17 +1465,23 @@ unset i M1B M1T
 ##
 ## main
 
-if {[catch {set gitdir [exec git rev-parse --git-dir]} err]} {
+set appname [lindex [file split $argv0] end]
+set gitdir {}
+
+if {[catch {set cdup [exec git rev-parse --show-cdup]} err]} {
 	show_msg {} . "Cannot find the git directory: $err"
 	exit 1
 }
-set cdup [exec git rev-parse --show-cdup]
 if {$cdup != ""} {
 	cd $cdup
 }
 unset cdup
 
-set appname [lindex [file split $argv0] end]
+if {[catch {set gitdir [exec git rev-parse --git-dir]} err]} {
+	show_msg {} . "Cannot find the git directory: $err"
+	exit 1
+}
+
 if {$appname == {git-citool}} {
 	set single_commit 1
 }