Do not call externalities without Ext being set (#3436)

* Do not call externalities without `Ext` being set

* Fix compare and set

* Bump runtime version.

* Bump hashmap_core

substrate/node/runtime/src/lib.rs

@@ -81,7 +81,7 @@ pub const VERSION: RuntimeVersion = RuntimeVersion {
 	// implementation changes and behavior does not, then leave spec_version as
 	// is and increment impl_version.
 	spec_version: 147,
-	impl_version: 148,
+	impl_version: 149,
 	apis: RUNTIME_API_VERSIONS,
 };