Centralise creation of a host_ca structure.

This will allow the central host_ca_new function to pre-populate the
structure with default values for the fields, so that once I add more
options to CA configuration they can take their default values when
loading a saved record from a previous PuTTY version.

utils/CMakeLists.txt

@@ -26,7 +26,7 @@ add_sources_from_current_dir(utils
   encode_utf8.c
   encode_wide_string_as_utf8.c
   fgetline.c
-  host_ca_free.c
+  host_ca_new_free.c
   host_strchr.c
   host_strchr_internal.c
   host_strcspn.c

utils/host_ca_new_free.c

@@ -2,6 +2,13 @@
 #include "misc.h"
 #include "storage.h"
 
+host_ca *host_ca_new(void)
+{
+    host_ca *hca = snew(host_ca);
+    memset(hca, 0, sizeof(*hca));
+    return hca;
+}
+
 void host_ca_free(host_ca *hca)
 {
     sfree(hca->name);