Fixes incorrect guest fd encoding

Surfaced when running sunfishcode/misc-tests. When trying to
truncate the file without the __WASI_RIGHT_PATH_FILESTAT_SET_SIZE
right, error __WASI_ENOTCAPABLE was correctly returned, however,
the guest fd pointer was not encoded to -1 in that case. This
commit fixes it by taking out the guest fd encoding out of the
conditional branch which turns out obsolete.

wasmtime-wasi-c/src/syscalls.rs

@@ -956,10 +956,8 @@ syscalls! {
             &mut host_fd,
         );
 
-        if u32::from(e) == host::__WASI_ESUCCESS {
-            trace!("     | *fd={:?}", host_fd);
-            encode_fd_byref(vmctx, fd, host_fd);
-        }
+        trace!("     | *fd={:?}", host_fd);
+        encode_fd_byref(vmctx, fd, host_fd);
 
         return_encoded_errno(e)
     }