MT#61856 parse_attribute_crypto: initialize `err` at least to something

Fixes:

../lib/loglib.h:54:17: warning: ‘err’ may be used uninitialized in this function [-Wmaybe-uninitialized]
   54 |                 __ilog(prio, "[%s] " fmt, log_level_names[system], ##__VA_ARGS__);                                              \
      |                 ^~~~~~
sdp.c:613:21: note: ‘err’ was declared here
  613 |         const char *err;
      |                     ^~~

sdp.c:734:9: warning: ‘err’ may be used uninitialized in this function [-Wmaybe-uninitialized]
  734 |         ilog(LOG_ERROR, "Failed to parse a=crypto attribute, ignoring: %s", err);
      |         ^
sdp.c:613:21: note: ‘err’ was declared here
  613 |         const char *err;
      |                     ^

Change-Id: I18c3c1d6f2d6d5643a61ef864116e1f3d5e1db95

daemon/sdp.c

@@ -610,7 +610,7 @@ static int parse_attribute_crypto(struct sdp_attribute *output) {
 	gsize ret;
 	str s;
 	uint32_t u32;
-	const char *err;
+	const char *err = NULL;
 
 	output->attr = ATTR_CRYPTO;
 
@@ -731,6 +731,8 @@ static int parse_attribute_crypto(struct sdp_attribute *output) {
 	return 0;
 
 error:
+	if (!err)
+		err = "generic error";
 	ilog(LOG_ERROR, "Failed to parse a=crypto attribute, ignoring: %s", err);
 	output->attr = ATTR_IGNORE;
 	return -1;