git-gui: Make Ctrl-T safe to use for conflicting files.

A previous patch added a check for conflict markers, which
is done when the file is about to be staged due to a click
on the icon. However, pressing Ctrl-T still immediately
stages the file without confirmation. This patch fixes it.

The check requires a loaded diff, so staging multiple files
at once won't work if they are unmerged.

Signed-off-by: Alexander Gavrilov <angavrilov@gmail.com>
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
diff --git a/git-gui.sh b/git-gui.sh
index 09ce410..4d52f02 100755
--- a/git-gui.sh
+++ b/git-gui.sh
@@ -2090,7 +2090,9 @@
 	if {$col == 0 && $y > 1} {
 		# Conflicts need special handling
 		if {[string first {U} $state] >= 0} {
-			merge_stage_workdir $path $w $lno
+			# $w must always be $ui_workdir, but...
+			if {$w ne $ui_workdir} { set lno {} }
+			merge_stage_workdir $path $lno
 			return
 		}