UI: Report detailed output errors for Replay Buffer

Same changes as 0c0ffb341cfb521473479cdcd391c3507b05cf46

UI/window-basic-main-outputs.cpp

@@ -1809,9 +1809,15 @@ bool AdvancedOutput::StartReplayBuffer()
 	}
 
 	if (!obs_output_start(replayBuffer)) {
+		QString error_reason;
+		const char *error = obs_output_get_last_error(replayBuffer);
+		if (error)
+			error_reason = QT_UTF8(error);
+		else
+			error_reason = QTStr("Output.StartFailedGeneric");
 		QMessageBox::critical(main,
 				      QTStr("Output.StartRecordingFailed"),
-				      QTStr("Output.StartFailedGeneric"));
+				      error_reason);
 		return false;
 	}