Fix possible crash in case of dictionary registration failed

It is possible that CREATE DICTIONARY will be failed with
CANNOT_SCHEDULE_TASK, and in this case loader will contain dangling
pointer, and on the next reload it will lead to crash.

Author: azat

src/Interpreters/ExternalLoader.cpp

@@ -1290,8 +1290,18 @@ scope_guard ExternalLoader::addConfigRepository(std::unique_ptr<IExternalLoaderC
     auto * ptr = repository.get();
     String name = ptr->getName();
 
-    config_files_reader->addConfigRepository(std::move(repository));
-    reloadConfig(name);
+    /// Avoid leaving dangling repository in case of reloadConfig() fails
+    /// (it can be possible in case of CANNOT_SCHEDULE_TASK)
+    try
+    {
+        config_files_reader->addConfigRepository(std::move(repository));
+        reloadConfig(name);
+    }
+    catch (...)
+    {
+        config_files_reader->removeConfigRepository(ptr);
+        throw;
+    }
 
     return [this, ptr, name]()
     {