git-gui: Paper bag fix "Commit->Revert" format arguments

The recent bug fix to correctly handle filenames with %s (or any
other valid Tcl format specifier) missed a \ on this line and
caused the remaining format arguments to not be supplied when we
updated the status bar.  This caused a Tcl error anytime the user
was trying to perform a file revert.

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

lib/index.tcl

@@ -168,7 +168,7 @@ proc checkout_index {msg pathList after} {
 
 	ui_status [format \
 		"%s... %i/%i files (%.2f%%)" \
-		$msg
+		$msg \
 		$update_index_cp \
 		$totalCnt \
 		0.0]