mmm: drop mmap on .Close() call.

eventstore/mmm/fuzz_test.go

@@ -40,7 +40,9 @@ func FuzzTest(f *testing.F) {
 
 		for i := range nlayers {
 			name := string([]byte{97 + byte(i)})
-			err = mmmm.EnsureLayer(name, &IndexingLayer{})
+			il := &IndexingLayer{}
+			err = mmmm.EnsureLayer(name, il)
+			defer il.Close()
 			require.NoError(t, err, "layer %s/%d", name, i)
 		}
 

eventstore/mmm/mmmm.go

@@ -329,4 +329,6 @@ func (b *MultiMmapManager) Close() {
 	for _, il := range b.layers {
 		il.Close()
 	}
+
+	syscall.Munmap(b.mmapf)
 }