libobs: Allow last encoder error for last output error

(This commit also modifies UI)

This makes it more trivial for encoder plugins to communicate to users
why specifically an encoder error might have occurred mid-stream.

UI/window-basic-main.cpp

@@ -6800,9 +6800,13 @@ void OBSBasic::StreamingStop(int code, QString last_error)
 	blog(LOG_INFO, STREAMING_STOP);
 
 	if (encode_error) {
+		QString msg =
+			last_error.isEmpty()
+				? QTStr("Output.StreamEncodeError.Msg")
+				: QTStr("Output.StreamEncodeError.Msg.LastError")
+					  .arg(last_error);
 		OBSMessageBox::information(
-			this, QTStr("Output.StreamEncodeError.Title"),
-			QTStr("Output.StreamEncodeError.Msg"));
+			this, QTStr("Output.StreamEncodeError.Title"), msg);
 
 	} else if (code != OBS_OUTPUT_SUCCESS && isVisible()) {
 		OBSMessageBox::information(this,
@@ -6949,9 +6953,13 @@ void OBSBasic::RecordingStop(int code, QString last_error)
 					QTStr("Output.RecordFail.Unsupported"));
 
 	} else if (code == OBS_OUTPUT_ENCODE_ERROR && isVisible()) {
-		OBSMessageBox::warning(
-			this, QTStr("Output.RecordError.Title"),
-			QTStr("Output.RecordError.EncodeErrorMsg"));
+		QString msg =
+			last_error.isEmpty()
+				? QTStr("Output.RecordError.EncodeErrorMsg")
+				: QTStr("Output.RecordError.EncodeErrorMsg.LastError")
+					  .arg(last_error);
+		OBSMessageBox::warning(this, QTStr("Output.RecordError.Title"),
+				       msg);
 
 	} else if (code == OBS_OUTPUT_NO_SPACE && isVisible()) {
 		OBSMessageBox::warning(this,