memory snapshots fix use after free on flatview copy

When restoring a snapshot with memory the flatview must be restored
before the memory reagions are filtered. Because the
AddressSpaceDispatcher also has pointer to the MemoryRegions and on copy
they need to be cleared. The memory_filter_subregions function frees
MemoryRegions which are not used at the time of the snapshot.

Author: PhilippTakacs

uc.c

@@ -2439,6 +2439,10 @@ uc_err uc_context_restore(uc_engine *uc, uc_context *context)
 
     if (uc->context_content & UC_CTL_CONTEXT_MEMORY) {
         uc->snapshot_level = context->snapshot_level;
+        if (!uc->flatview_copy(uc, uc->address_space_memory.current_map,
+                               context->fv, true)) {
+            return UC_ERR_NOMEM;
+        }
         ret = uc_restore_latest_snapshot(uc);
         if (ret != UC_ERR_OK) {
             restore_jit_state(uc);
@@ -2447,10 +2451,6 @@ uc_err uc_context_restore(uc_engine *uc, uc_context *context)
         uc_snapshot(uc);
         uc->ram_list.freed = context->ramblock_freed;
         uc->ram_list.last_block = context->last_block;
-        if (!uc->flatview_copy(uc, uc->address_space_memory.current_map,
-                               context->fv, true)) {
-            return UC_ERR_NOMEM;
-        }
         uc->tcg_flush_tlb(uc);
     }