libtiff: tiffmedian: avoid zero num_colors, fixes #477

From 3c774f1903062eb53ae06274f56e521a925ba996 Mon Sep 17 00:00:00 2001
From: Su_Laus <[EMAIL REDACTED]>
Date: Thu, 12 Jan 2023 22:33:46 +0100
Subject: [PATCH] tiffmedian: avoid zero num_colors, fixes #477

---
 tools/tiffmedian.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/tools/tiffmedian.c b/tools/tiffmedian.c
index 8225970c..334566a4 100644
--- a/tools/tiffmedian.c
+++ b/tools/tiffmedian.c
@@ -144,10 +144,15 @@ int main(int argc, char *argv[])
                 num_colors = atoi(optarg);
                 if (num_colors > MAX_CMAP_SIZE)
                 {
-                    fprintf(stderr, "-c: colormap too big, max %d\n",
+                    fprintf(stderr, "-C: colormap too big, max %d\n",
                             MAX_CMAP_SIZE);
                     usage(EXIT_FAILURE);
                 }
+                if (num_colors < 2)
+                {
+                    fprintf(stderr, "-C: colormap too small, min %d\n", 2);
+                    usage(EXIT_FAILURE);
+                }
                 break;
             case 'f': /* dither */
                 dither = 1;