Main, db/Glue: improve error messages

src/Main.cxx

@@ -203,7 +203,11 @@ glue_db_init_and_load(void)
 				   "because the database does not need it");
 	}
 
-	instance->database->Open();
+	try {
+		instance->database->Open();
+	} catch (...) {
+		std::throw_with_nested(std::runtime_error("Failed to open database plugin"));
+	}
 
 	if (!instance->database->IsPlugin(simple_db_plugin))
 		return true;

src/db/DatabaseGlue.cxx

@@ -37,5 +37,10 @@ DatabaseGlobalInit(EventLoop &loop, DatabaseListener &listener,
 		throw FormatRuntimeError("No such database plugin: %s",
 					 plugin_name);
 
-	return plugin->create(loop, listener, block);
+	try {
+		return plugin->create(loop, listener, block);
+	} catch (...) {
+		std::throw_with_nested(FormatRuntimeError("Failed to initialize database plugin '%s'",
+							  plugin_name));
+	}
 }