Handle IO error on document save (#961)

* Add try/except to document replace call
* Try the os.replace command 5 times
* Just use else condition on for loop instead
* Make the exceptions explicitly OSError
* Revert the os.replace loop, as this is not the issue

novelwriter/core/document.py

@@ -162,7 +162,11 @@ class NWDoc():
 
         # If we're here, the file was successfully saved, so we can
         # replace the temp file with the actual file
-        os.replace(docTemp, docPath)
+        try:
+            os.replace(docTemp, docPath)
+        except OSError as exc:
+            self._docError = formatException(exc)
+            return False
 
         self._prevHash = sha256sum(docPath)
         self._currHash = self._prevHash