fs/io/FileOutputStream: don't auto-delete file on WIN32

The file handle is never reset to INVALID_HANDLE_VALUE, and thus the
destructor will assume the operation shall be cancelled and will
delete the temporary file.

This was a major breakage for saving the database file and the state
file.

src/fs/io/FileOutputStream.cxx

@@ -62,6 +62,7 @@ FileOutputStream::Commit(gcc_unused Error &error)
 	assert(IsDefined());
 
 	CloseHandle(handle);
+	handle = INVALID_HANDLE_VALUE;
 	return true;
 }
 
@@ -71,6 +72,7 @@ FileOutputStream::Cancel()
 	assert(IsDefined());
 
 	CloseHandle(handle);
+	handle = INVALID_HANDLE_VALUE;
 	RemoveFile(path);
 }