Gracefully degrade when not available.

Sigalgs is not a critical extension, so gracefully degrade when not available.

Author: Jean-Daniel Dupas

src/OpenSSL/SSL.py

@@ -1217,6 +1217,9 @@ def set_sigalgs_list(self, sigalgs_list):
         :param bytes sigalgs_list: An OpenSSL signature algorithms list.
         :return: None
         """
+        if not _lib.Cryptography_HAS_SIGALGS:
+            return
+
         sigalgs_list = _text_to_bytes_and_warn("sigalgs_list", sigalgs_list)
 
         if not isinstance(sigalgs_list, bytes):
@@ -2047,6 +2050,9 @@ def get_sigalgs(self):
         :return: A list of SignatureScheme (int) as defined by RFC 8446.
         """
         sigalgs = []
+        if not _lib.Cryptography_HAS_SIGALGS:
+            return sigalgs
+
         rsign = _ffi.new("unsigned char *")
         rhash = _ffi.new("unsigned char *")
         for i in count():