git-gui: Brown paper bag fix division by 0 in blame

If we generate a blame status string before we have obtained
any annotation data at all from the input file, or if the input
file is empty, our total_lines will be 0.  This causes a division
by 0 error when we blindly divide by the 0 to compute the total
percentage of lines loaded.  Instead we should report 0% done.

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

git-gui.sh

@@ -3604,12 +3604,14 @@ proc read_blame_incremental {fd w w_load w_cmit w_line w_file} {
 proc blame_incremental_status {w} {
 	global blame_status blame_data
 
+	set have  $blame_data($w,blame_lines)
+	set total $blame_data($w,total_lines)
+	set pdone 0
+	if {$total} {set pdone [expr {100 * $have / $total}]}
+
 	set blame_status($w) [format \
 		"Loading annotations... %i of %i lines annotated (%2i%%)" \
-		$blame_data($w,blame_lines) \
-		$blame_data($w,total_lines) \
-		[expr {100 * $blame_data($w,blame_lines)
-			/ $blame_data($w,total_lines)}]]
+		$have $total $pdone]
 }
 
 proc blame_click {w w_cmit w_line w_file cur_w pos} {