Fix: Signature validation did not close its file.

src/signature.cpp

@@ -205,6 +205,7 @@ static bool _ValidateSignatureFile(const std::string &filename)
 
 	std::string text(filesize, '\0');
 	size_t len = fread(text.data(), filesize, 1, f);
+	FioFCloseFile(f);
 	if (len != 1) {
 		Debug(misc, 0, "Failed to validate signature: failed to read file: {}", filename);
 		return false;