Make the BIOS linker optional in acpi_table_end().
This makes it possible to call for example
acpi_build_madt() from outside the ACPI table builder context.

Signed-off-by: Oliver Steffen <osteffen@redhat.com>
---
 hw/acpi/aml-build.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/hw/acpi/aml-build.c b/hw/acpi/aml-build.c
index 2d5826a8f1..ed86867ae3 100644
--- a/hw/acpi/aml-build.c
+++ b/hw/acpi/aml-build.c
@@ -1748,8 +1748,11 @@ void acpi_table_end(BIOSLinker *linker, AcpiTable *desc)
      */
     memcpy(len_ptr, &table_len_le, sizeof table_len_le);
 
-    bios_linker_loader_add_checksum(linker, ACPI_BUILD_TABLE_FILE,
-        desc->table_offset, table_len, desc->table_offset + checksum_offset);
+    if (linker != NULL) {
+        bios_linker_loader_add_checksum(linker, ACPI_BUILD_TABLE_FILE,
+                                        desc->table_offset, table_len,
+                                        desc->table_offset + checksum_offset);
+    }
 }
 
 void *acpi_data_push(GArray *table_data, unsigned size)
-- 
2.52.0