Fix: Rollback on create_credential privkey error

If the private key checks in create_credential fail, the SQL
transaction is now rolled back.

This fixes SQL transaction errors and possible incomplete
credentials being created if there are multiple GMP commands per
connection and one of them is create_credential failing because of
the private key.

src/manage_sql.c

@@ -35916,7 +35916,10 @@ create_credential (const char* name, const char* comment, const char* login,
       if (key_private)
         key_private_truncated = truncate_private_key (key_private);
       else
-        return 3;
+        {
+          sql_rollback ();
+          return 3;
+        }
 
       generated_key_public = gvm_ssh_public_from_private
                                 (key_private_truncated
@@ -35926,6 +35929,7 @@ create_credential (const char* name, const char* comment, const char* login,
       if (generated_key_public == NULL)
         {
           g_free (key_private_truncated);
+          sql_rollback ();
           return 3;
         }
       g_free (generated_key_public);