Fix bind() before connect, and case that can happen in SMB

Author: gpotter2

scapy/layers/msrpce/rpcclient.py

@@ -148,7 +148,10 @@ def from_smblink(cls, smbcli, smb_kwargs={}, **kwargs):
 
     @property
     def session(self) -> DceRpcSession:
-        return self.sock.session
+        try:
+            return self.sock.session
+        except AttributeError:
+            raise ValueError("Client is not connected ! Please connect()")
 
     def connect(
         self,
@@ -485,7 +488,8 @@ def _check_bind_context(self, interface, contexts) -> bool:
         for i, ctx in enumerate(contexts):
             if ctx.result == 0:
                 # Context was accepted. Remove all others from cache
-                self.contexts[interface] = [self.contexts[interface][i]]
+                if len(self.contexts[interface]) != 1:
+                    self.contexts[interface] = [self.contexts[interface][i]]
                 return True
 
         return False