client session BUGFIX be ready for context creation fail

Although it should not happen under standard conditions.
diff --git a/src/session_client_tls.c b/src/session_client_tls.c
index 575fd95..37f9d4e 100644
--- a/src/session_client_tls.c
+++ b/src/session_client_tls.c
@@ -561,6 +561,11 @@
         } else {
             ctx = ly_ctx_new(SCHEMAS_DIR);
         }
+        /* definitely should not happen, but be ready */
+        if (!ctx && !(ctx = ly_ctx_new(NULL))) {
+            /* that's just it */
+            goto fail;
+        }
     } else {
         session->flags |= NC_SESSION_SHAREDCTX;
     }
@@ -626,6 +631,11 @@
         } else {
             ctx = ly_ctx_new(SCHEMAS_DIR);
         }
+        /* definitely should not happen, but be ready */
+        if (!ctx && !(ctx = ly_ctx_new(NULL))) {
+            /* that's just it */
+            goto fail;
+        }
     } else {
         session->flags |= NC_SESSION_SHAREDCTX;
     }