another fix of version string parse

setup.py

@@ -19,7 +19,10 @@ SPCONV_FORCE_BUILD_CUDA = os.getenv("SPCONV_FORCE_BUILD_CUDA")
 
 PYTHON_VERSION = "{}.{}".format(sys.version_info.major, sys.version_info.minor)
 
-PYTORCH_VERSION = torch.__version__[:torch.__version__.find("+")]
+remove_plus = torch.__version__.find("+")
+PYTORCH_VERSION = torch.__version__
+if remove_plus != -1:
+    PYTORCH_VERSION = torch.__version__[:remove_plus]
 PYTORCH_VERSION = list(map(int, PYTORCH_VERSION.split(".")))
 PYTORCH_VERSION_NUMBER = PYTORCH_VERSION[0] * 10000 + PYTORCH_VERSION[1] * 100 + PYTORCH_VERSION[2]