qemu: Get default hugepage size only if needed

Fixes: 6864d8f740

Hugepages don't work in session mode but when building memory
part of command line we query for the default size anyway. This
breaks creating domains under session daemon. Query the page size
only if it's clear we need hugepages.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Erik Skultety <eskultet@redhat.com>

src/qemu/qemu_command.c

@@ -3573,7 +3573,7 @@ qemuBuildMemoryBackendProps(virJSONValuePtr *backendProps,
         pagesize = 0;
         needHugepage = false;
         useHugepage = false;
-    } else if (pagesize == 0) {
+    } else if (useHugepage && pagesize == 0) {
         if (qemuBuildMemoryGetDefaultPagesize(cfg, &pagesize) < 0)
             goto cleanup;
     }