Limit match length

Avoids quadratic runtime and potential DoS with adversarial inputs

Ref oobabooga/text-generation-webui#6047

Author: p-e-w

mistralrs-core/src/sampler.rs

@@ -498,7 +498,8 @@ impl Sampler {
 
                 let mut match_length = 1;
 
-                loop {
+                // Limit match length to avoid quadratic runtime and potential DoS with adversarial inputs.
+                while match_length < 50 {
                     if match_length > i {
                         // Start of input
                         break;