Avoid exporting bogus (empty) data if empty selection is used

This is already correct in the rsa_kmgmt.c but other
implementations are wrong.

Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Paul Dale <pauli@openssl.org>
Reviewed-by: Todd Short <todd.short@me.com>
(Merged from #21519)

(cherry picked from commit 1ae4678)

providers/implementations/keymgmt/dh_kmgmt.c

@@ -222,6 +222,9 @@ static int dh_export(void *keydata, int selection, OSSL_CALLBACK *param_cb,
     if (!ossl_prov_is_running() || dh == NULL)
         return 0;
 
+    if ((selection & DH_POSSIBLE_SELECTIONS) == 0)
+        return 0;
+
     tmpl = OSSL_PARAM_BLD_new();
     if (tmpl == NULL)
         return 0;

providers/implementations/keymgmt/dsa_kmgmt.c

@@ -223,6 +223,9 @@ static int dsa_export(void *keydata, int selection, OSSL_CALLBACK *param_cb,
     if (!ossl_prov_is_running() || dsa == NULL)
         return 0;
 
+    if ((selection & DSA_POSSIBLE_SELECTIONS) == 0)
+        return 0;
+
     tmpl = OSSL_PARAM_BLD_new();
     if (tmpl == NULL)
         return 0;

providers/implementations/keymgmt/ecx_kmgmt.c

@@ -238,6 +238,9 @@ static int ecx_export(void *keydata, int selection, OSSL_CALLBACK *param_cb,
     if (!ossl_prov_is_running() || key == NULL)
         return 0;
 
+    if ((selection & OSSL_KEYMGMT_SELECT_KEYPAIR) == 0)
+        return 0;
+
     tmpl = OSSL_PARAM_BLD_new();
     if (tmpl == NULL)
         return 0;

providers/implementations/keymgmt/mac_legacy_kmgmt.c

@@ -281,6 +281,9 @@ static int mac_export(void *keydata, int selection, OSSL_CALLBACK *param_cb,
     if (!ossl_prov_is_running() || key == NULL)
         return 0;
 
+    if ((selection & OSSL_KEYMGMT_SELECT_PRIVATE_KEY) == 0)
+        return 0;
+
     tmpl = OSSL_PARAM_BLD_new();
     if (tmpl == NULL)
         return 0;