Probably fix the error running on windows

I just copy the code in the folder `saicinpainting`  to my code repository, since I just want to adopt `FFC_BN_FLU` layer in my net. Then it occurs an error:
```bash
  File "C:\Users\xx\tmp\saicinpainting\utils.py", line 104, in <module>
    def register_debug_signal_handlers(sig=signal.SIGUSR1, handler=print_traceback_handler):
AttributeError: module 'signal' has no attribute 'SIGUSR1'
```

This patch fixes the error.

Author: Zhaoyi-Yan

saicinpainting/utils.py

@@ -13,6 +13,9 @@
 
 LOGGER = logging.getLogger(__name__)
 
+import platform
+if platform.system() != 'Linux':
+    signal.SIGUSR1 = 1
 
 def check_and_warn_input_range(tensor, min_value, max_value, name):
     actual_min = tensor.min()