zsock: Check native socket in zsock_resolve before ZMQ socket

Especially in Windows (at least on builds using MSVC), `zsock_resolve`
randomly (but quite often) segfaults if the passed pointer is actually
pointing to a native `SOCKET` instead of zactor, zsock, or a ZMQ socket.
This happens because `zmq_getsockopt` tries to check if, after casting,
the pointer points to an object with specific tag (`check_tag()`).
Unfortunately, reading this area of memory is often an access violation
if the pointer actually pointed to a `SOCKET` (which is a smaller data
type).

It seems that checking if the pointer is to a native socket first before
checking if it is a ZMQ socket fixes this, so these checks were
reordered.

Resolves #2300

Author: oko256

src/zsock.c

@@ -1845,13 +1845,10 @@ zsock_resolve (void *self)
     if (zsock_is (self))
         return ((zsock_t *) self)->handle;
 
-    //  Check if we have a valid ZMQ socket by probing the socket type
-    int type;
-    size_t option_len = sizeof (int);
-    if (zmq_getsockopt (self, ZMQ_TYPE, &type, &option_len) == 0)
-        return self;
-
     //  Check if self is a valid FD or socket FD
+    //  We need to check this before zmq_getsockopt, because tag check may
+    //  cause a segfault if we are checking a native SOCKET (since the data
+    //  type is smaller than the full object).
     //  TODO: this code should move to zsys_isfd () as we don't like
     //  non-portable code outside of that class.
     int sock_type = -1;
@@ -1866,6 +1863,13 @@ zsock_resolve (void *self)
     if (rc == 0 || (rc == -1 && errno == ENOTSOCK))
         return NULL;        //  It's a socket FD or FD
 #endif
+
+    //  Check if we have a valid ZMQ socket by probing the socket type
+    int type;
+    size_t option_len = sizeof (int);
+    if (zmq_getsockopt (self, ZMQ_TYPE, &type, &option_len) == 0)
+        return self;
+
     //  Socket appears to be something else, return it as-is
     return self;
 }