Added explicitly typed exception for Template validation

Author: Lyrcaxis

LLama/Exceptions/RuntimeError.cs

@@ -77,6 +77,21 @@ public MissingTemplateException(string message)
     } 
 }
 
+/// <summary>
+/// `llama_decode` return a non-zero status code
+/// </summary>
+public class TemplateNotFoundException
+    : RuntimeError
+{
+    /// <inheritdoc />
+    public TemplateNotFoundException(string name)
+        : base($"llama_model_chat_template failed: Tried to retrieve template '{name}' but it couldn't be found.\n" +
+                                            $"This might mean that the model was exported incorrectly, or that this is a base model that contains no templates.\n" +
+                                            $"This exception can be disabled by passing 'strict=false' as a parameter when retrieving the template.")
+    {
+    } 
+}
+
 /// <summary>
 /// `llama_get_logits_ith` returned null, indicating that the index was invalid
 /// </summary>

LLama/Native/SafeLlamaModelHandle.cs

@@ -614,9 +614,7 @@ internal IReadOnlyDictionary<string, string> ReadMetadata()
                 if (bytesPtr == null)
                 {
                     if (strict)
-                        throw new Exception($"Tried to retrieve template for '{name}' but no templates were found.\n" +
-                                            $"This might mean that the model was exported incorrectly, or that this is a base model that contains no template.\n" +
-                                            $"This exception can be disabled by passing 'strict=false' as a parameter when retrieving the template.");
+                        throw new TemplateNotFoundException(name ?? "default template");
                     else
                         return null;