_libssh2_recv(): handle ENOENT error as EAGAIN

A sftp session failed with error "failure establishing ssh session" on
Solaris and HP-UX. Sometimes the first recv() function call sets errno
to ENOENT. In the man pages for recv of Solaris and HP-UX the error
ENOENT is not documented.

I tested Solaris SPARC and x86, HP-UX i64, AIX, Windows and Linux.

src/misc.c

@@ -108,8 +108,14 @@ _libssh2_recv(libssh2_socket_t sock, void *buffer, size_t length, int flags)
             return -errno;
     }
 #else
-    if (rc < 0 )
+    if (rc < 0 ){
+        /* Sometimes the first recv() function call sets errno to ENOENT on
+           Solaris and HP-UX */
+        if ( errno == ENOENT )
+            return -EAGAIN;
+        else
             return -errno;
+    }
 #endif
     return rc;
 }