HELLO: Zero out page tables after allocating, before using

src/hello/hello.d

@@ -4,6 +4,7 @@ import scratch;
 import hulk.bootinfo;
 import hos.page_table;
 import hos.cpu;
+import hos.memory;
 
 __gshared EFI_SYSTEM_TABLE * st;
 __gshared BootInfo bootinfo;
@@ -124,7 +125,9 @@ private bool get_memory_map()
 
 private PageTableEntry * new_page_table()
 {
-    return cast(PageTableEntry *)scratch_alloc(1u);
+    PageTableEntry * pt = cast(PageTableEntry *)scratch_alloc(1u);
+    memset64(pt, 0u, 512);
+    return pt;
 }
 
 private void map(ulong source_page, ulong dest_page, PageTableEntry * pt_base)