mergetool: Don't error out in the merge case where the local file is deleted

If the file we are trying to merge resolve is in git-ls-files -u, then
skip the file existence test.  If the file isn't reported in
git-ls-files, then check to see if the file exists or not to give an
appropriate error message.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
diff --git a/git-mergetool.sh b/git-mergetool.sh
index 3401823..fa301ad 100755
--- a/git-mergetool.sh
+++ b/git-mergetool.sh
@@ -109,14 +109,13 @@
 merge_file () {
     path="$1"
 
-    if test ! -f "$path" ; then
-	echo "$path: file not found"
-	exit 1
-    fi
-
     f=`git-ls-files -u -- "$path"`
     if test -z "$f" ; then
-	echo "$path: file does not need merging"
+        if test ! -f "$path" ; then
+	    echo "$path: file not found"
+	else
+	    echo "$path: file does not need merging"
+	fi
 	exit 1
     fi