Resolve saveAs Conflict

src/Gifitti/Gifitti/View_Models/MainForm.cs

@@ -178,7 +178,7 @@ namespace Gifitti.View_Models
         {
             int start = 0;
             bool pass = int.TryParse(textBox1.Text, out start);
-            if (pass & start >= 0)
+            if (pass && start >= 0 && start < gm.numberOfFrames)
             {
                 gm.startFrame = start;
             }