context BUGFIX searching for the latest revision

when the latest revision is already in the context and searching via
import callback and searchapths provides an older revisions, the newest
revision from the context must be used. On the other hand, when some
revision is present in the context (and callback/searchpaths were not
used to get it), the callback/searchpaths should be tried to get a newer
revision.
diff --git a/src/tree_schema_helpers.c b/src/tree_schema_helpers.c
index c6c4511..9259b6f 100644
--- a/src/tree_schema_helpers.c
+++ b/src/tree_schema_helpers.c
@@ -678,11 +678,13 @@
 {
     struct lysp_load_module_check_data *info = data;
     const char *filename, *dot, *rev, *name;
+    uint8_t latest_revision;
     size_t len;
     struct lysp_revision *revs;
 
     name = mod ? mod->mod->name : submod->name;
     revs = mod ? mod->revs : submod->revs;
+    latest_revision = mod ? mod->mod->latest_revision : submod->latest_revision;
 
     if (info->name) {
         /* check name of the parsed model */
@@ -698,6 +700,9 @@
                    revs ? revs[0].date : "none", info->revision);
             return LY_EINVAL;
         }
+    } else if (!latest_revision) {
+        /* do not log, we just need to drop the schema and use the latest revision from the context */
+        return LY_EEXIST;
     }
     if (submod) {
         assert(info->submoduleof);
@@ -804,7 +809,7 @@
     LYS_INFORMAT format = LYS_IN_UNKNOWN;
     void (*module_data_free)(void *module_data, void *user_data) = NULL;
     struct lysp_load_module_check_data check_data = {0};
-    struct lys_module *m;
+    struct lys_module *m = NULL;
 
     assert(mod);
 
@@ -824,6 +829,11 @@
             /* get the requested module of the latest revision in the context */
 latest_in_the_context:
             *mod = (struct lys_module*)ly_ctx_get_module_latest(ctx, name);
+            if (*mod && (*mod)->latest_revision == 1) {
+                /* let us now search with callback and searchpaths to check if there is newer revision outside the context */
+                m = *mod;
+                *mod = NULL;
+            }
         }
     }
 
@@ -871,9 +881,12 @@
             }
         }
 
-        if ((*mod) && !revision && ((*mod)->latest_revision == 1)) {
-            /* update the latest_revision flag - here we have selected the latest available schema,
-             * consider that even the callback provides correct latest revision */
+        /* update the latest_revision flag - here we have selected the latest available schema,
+         * consider that even the callback provides correct latest revision */
+        if (!(*mod) && m) {
+            m->latest_revision = 2;
+            *mod = m;
+        } else if ((*mod) && !revision && ((*mod)->latest_revision == 1)) {
             (*mod)->latest_revision = 2;
         }
     } else {