Fix in ext.py (index error on system without GPU) (#594)

* Update README.md

* Fix in ext.py (index error on system without GPU)

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Co-authored-by: turboderp <[email protected]>

Author: MischaPanch

exllamav2/ext.py

@@ -39,6 +39,8 @@ def maybe_set_arch_list_env():
         arch = f'{capability[0]}.{capability[1]}'
         if arch not in arch_list:
             arch_list.append(arch)
+    if not arch_list:
+        return
     arch_list = sorted(arch_list)
     arch_list[-1] += '+PTX'