handle "filter result size = 0" without crashing

Program.cs

@@ -647,7 +647,11 @@ public class Game : GameWindow {
     }
 
     // Make sure the photoIndex is actually valid.
-    photoIndex = Math.Clamp(photoIndex, 0, photos.Count - 1);
+    if (photos.Count == 0) {
+      photoIndex = 0;
+    } else {
+      photoIndex = Math.Clamp(photoIndex, 0, photos.Count - 1);
+    }
 
     // Handle presses of the "rating" keys -- 0-5 and `.
     // A normal press just sets the rating of the current photo.
@@ -683,7 +687,9 @@ public class Game : GameWindow {
       if (shifted) {
         FilterByRating(rating);
       } else {
-        photos[photoIndex].Rating = rating;
+        if (photos.Count > 0) {
+          photos[photoIndex].Rating = rating;
+        }
       }
     }
 
@@ -714,7 +720,7 @@ public class Game : GameWindow {
 
   void FilterByRating(int rating) {
     Console.WriteLine("filter to " + rating);
-    Photo previouslyActive = photos[photoIndex];
+    Photo previouslyActive = photos.Count > 0 ? photos[photoIndex] : allPhotos[0];
     photos = allPhotos.Where(p => p.Rating >= rating).ToList();
     // Move photoIndex to wherever the previously active photo was, or if it
     // was filtered out, to whichever unfiltered photo comes before it. This
@@ -773,8 +779,8 @@ public class Game : GameWindow {
     // string[] files = Directory.GetFiles(@"c:\users\colin\pictures\photos\2023\07\14\");
     // string[] files = Directory.GetFiles(@"G:\DCIM\100EOSR6\");
     // string[] files = Directory.GetFiles(@"C:\Users\colin\Pictures\photos\2018\06\23");
-    // string[] files = Directory.GetFiles(@"C:\Users\colin\Desktop\Germany all\104D7000");
-    string[] files = Directory.GetFiles(@"C:\Users\colin\Desktop\many-birds\");
+    string[] files = Directory.GetFiles(@"C:\Users\colin\Desktop\Germany all\104D7000");
+    // string[] files = Directory.GetFiles(@"C:\Users\colin\Desktop\many-birds\");
 
     for (int i = 0; i < files.Count(); i++) {
       string file = files[i];
@@ -843,6 +849,16 @@ public class Game : GameWindow {
     GL.BindBuffer(BufferTarget.ArrayBuffer, VertexBufferObject);
     GL.ActiveTexture(TextureUnit.Texture0);
 
+    if (photos.Count > 0) {
+      DrawPhotos();
+    } else {
+      DrawText("No photos found.", 10, 10);
+    }
+
+    SwapBuffers();
+  }
+
+  void DrawPhotos() {
     Photo activePhoto = photos[photoIndex];
     Texture active = activePhoto.Texture();
 
@@ -892,8 +908,6 @@ public class Game : GameWindow {
     if (activePhoto.Loaded) {
       DrawText($"{(scale * 100):F1}%", geometry.StatusBox.Min.X, geometry.StatusBox.Min.Y + statusPadding);
     }
-
-    SwapBuffers();
   }
 
   void DrawTexture(Texture texture, int x, int y) {