conf: Restore the XML parser context in virDomainMemoryDefParseXML

After parsing the memory device XML the function would not restore the
XML parser context causing invalid XPath starting point for the rest of
the elements. This is a regression since 3e4230d2.

The test case addition uses the <idmap> element that is currently unused
by qemu, but parsed after the memory device definition and formatted
always.

Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1223631Signed-off-by: NLuyao Huang <lhuang@redhat.com>
Signed-off-by: NPeter Krempa <pkrempa@redhat.com>

src/conf/domain_conf.c

@@ -11836,6 +11836,7 @@ virDomainMemoryDefParseXML(xmlNodePtr memdevNode,
     if (virDomainDeviceInfoParseXML(memdevNode, NULL, &def->info, flags) < 0)
         goto error;
 
+    ctxt->node = save;
     return def;
 
  error:

tests/qemuxml2argvdata/qemuxml2argv-memory-hotplug-dimm.xml

@@ -9,6 +9,10 @@
     <type arch='i686' machine='pc'>hvm</type>
     <boot dev='hd'/>
   </os>
+  <idmap>
+    <uid start='0' target='1000' count='10'/>
+    <gid start='0' target='1000' count='10'/>
+  </idmap>
   <cpu>
     <topology sockets='2' cores='1' threads='1'/>
     <numa>