stream-clone: bail-out earlier if stream clone is not requested

The `canperformstreamclone` function is bit messy. However it seems clearer to
me to check if a stream-clone have been requested by the client or the server
at all, before checking if a compatible protocol can be negotiated with the
server.

So I am doing some gratuitous movement so reorder conditional.

mercurial/streamclone.py

@@ -69,6 +69,16 b' def canperformstreamclone(pullop, bundle'
     repo = pullop.repo
     remote = pullop.remote
 
+    # should we consider streaming clone at all ?
+    streamrequested = pullop.streamclonerequested
+    # If we don't have a preference, let the server decide for us. This
+    # likely only comes into play in LANs.
+    if streamrequested is None:
+        # The server can advertise whether to prefer streaming clone.
+        streamrequested = remote.capable(b'stream-preferred')
+    if not streamrequested:
+        return False, None
+
     # Streaming clone only works on an empty destination repository
     if len(repo):
         return False, None
@@ -92,17 +102,6 b' def canperformstreamclone(pullop, bundle'
     elif bundle2 and not bundle2supported:
         return False, None
 
-    streamrequested = pullop.streamclonerequested
-
-    # If we don't have a preference, let the server decide for us. This
-    # likely only comes into play in LANs.
-    if streamrequested is None:
-        # The server can advertise whether to prefer streaming clone.
-        streamrequested = remote.capable(b'stream-preferred')
-
-    if not streamrequested:
-        return False, None
-
     # In order for stream clone to work, the client has to support all the
     # requirements advertised by the server.
     #