qt: Use gpgrt_asprintf instead of qstrdup

* lang/qt/src/dn.cpp (parse_dn_part): Use gpgrt_asprintf instead
of qstrdup.

--
This fixes a new / free mismatch because qstrdup uses new and
the allocated parts are freed with free. Similar to: a09ed3f2

lang/qt/src/dn.cpp

@@ -37,7 +37,7 @@
 
 #include "dn.h"
 
-#include <strings.h>
+#include <gpg-error.h>
 
 static const struct {
     const char *name;
@@ -167,7 +167,7 @@ parse_dn_part(DnPair *array, const unsigned char *string)
     for (unsigned int i = 0; i < numOidMaps; ++i)
         if (!strcasecmp((char *)p, oidmap[i].oid)) {
             free(p);
-            p = qstrdup(oidmap[i].name);
+            gpgrt_asprintf(&p, oidmap[i].name);
             break;
         }
     array->key = p;