[Memory] Trigger watches when making pages writable, not the other way around

src/xenia/kernel/xboxkrnl/xboxkrnl_io.cc

@@ -170,8 +170,8 @@ dword_result_t NtReadFile(dword_t file_handle, dword_t event_handle,
   if (XSUCCEEDED(result)) {
     if (true || file->is_synchronous()) {
       // some games NtReadFile() directly into texture memory
-      // TODO(rick): better checking of physical address
-      if (buffer.guest_address() >= 0xA0000000) {
+      auto heap = kernel_memory()->LookupHeap(buffer.guest_address());
+      if (heap && heap->IsGuestPhysicalHeap()) {
         kernel_memory()->TriggerWatches(buffer.guest_address(), buffer_length,
                                         true, true);
       }