fs: returns EBADF on negative file descriptor (#1391)

This changes file descriptors from uint32 to int32 and the
corresponding file table to reject negative values. This ensures
invalid values aren't mistaken for very large descriptor entries, which
can use a lot of memory as the table implementation isn't designed to
be sparse.

See https://pubs.opengroup.org/onlinepubs/9699919799/functions/dirfd.html#tag_16_90

Signed-off-by: Adrian Cole <adrian@tetrate.io>

internal/wasm/module_instance.go

@@ -142,7 +142,7 @@ func (m *ModuleInstance) setExitCode(exitCode uint32, flag exitCodeFlag) bool {
 // Multiple calls to this function is safe.
 func (m *ModuleInstance) ensureResourcesClosed(ctx context.Context) (err error) {
 	if sysCtx := m.Sys; sysCtx != nil { // nil if from HostModuleBuilder
-		if err = sysCtx.FS().Close(ctx); err != nil {
+		if err = sysCtx.FS().Close(); err != nil {
 			return err
 		}
 		m.Sys = nil