smb: fix memory leak on early failure

... by making sure connection related data (->share) is stored in the
connection and not in the easy handle.

Detected by OSS-fuzz
Bug: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=9369
Fixes #2769
Closes #2810

lib/smb.h

@@ -35,6 +35,7 @@ struct smb_conn {
   enum smb_conn_state state;
   char *user;
   char *domain;
+  char *share;
   unsigned char challenge[8];
   unsigned int session_key;
   unsigned short uid;