API: Fix finish_reason returns

OAI expects finish_reason to be "stop" or "length" (there are others,
but they're not in the current scope of this project).

Make all completions and chat completions responses return this
from the model generation itself rather than putting a placeholder.

Signed-off-by: kingbri <bdashore3@proton.me>

backends/exllamav2/model.py

@@ -605,6 +605,9 @@ class ExllamaV2Container:
             joined_generation["generation_tokens"] = unwrap(
                 generations[-1].get("generated_tokens"), 0
             )
+            joined_generation["finish_reason"] = unwrap(
+                generations[-1].get("finish_reason"), "stop"
+            )
 
         return joined_generation
 
@@ -1004,6 +1007,10 @@ class ExllamaV2Container:
                 last_chunk_time = now
 
             if eos or generated_tokens == max_tokens:
+                finish_reason = "length" if generated_tokens == max_tokens else "stop"
+                generation = {"finish_reason": finish_reason}
+                yield generation
+
                 break
 
         # Print response