plugins BUGFIX properly check extension instance

... even when they are from different contexts.

Fixes sysrepo/sysrepo#1225
diff --git a/src/plugins.c b/src/plugins.c
index d239dee..4045fd5 100644
--- a/src/plugins.c
+++ b/src/plugins.c
@@ -442,8 +442,17 @@
 
     /* search for the extension instance */
     for (index = 0; index < ext_size; index++) {
-        if (ext[index]->def == def) {
-            return index;
+        if (ext[index]->module->ctx == def->module->ctx) {
+            /* from the same context */
+            if (ext[index]->def == def) {
+                return index;
+            }
+        } else {
+            /* from different contexts */
+            if (ly_strequal0(ext[index]->def->name, def->name)
+                    && ly_strequal0(lys_main_module(ext[index]->def->module)->name, lys_main_module(def->module)->name)) {
+                return index;
+            }
         }
     }