ImportExport: Avoid duplicate warnings

In addition to 'addWarning()' 'addWarningOnce()' only adds a warning to
the list of warnings if the warning is not yet in the list.

Author: dl3sdo

src/fileformats/file_import_export.cpp

@@ -1,7 +1,7 @@
 /*
  *    Copyright 2012, 2013 Pete Curtis
  *    Copyright 2013, 2014 Thomas Schöps
- *    Copyright 2013-2020 Kai Pastor
+ *    Copyright 2013-2020, 2024 Kai Pastor
  *
  *    This file is part of OpenOrienteering.
  *
@@ -21,6 +21,7 @@
 
 #include "file_import_export.h"
 
+#include <algorithm>
 #include <exception>
 #include <memory>
 #include <utility>
@@ -84,6 +85,13 @@ void ImportExport::setOption(const QString& name, const QVariant& value)
 }
 
 
+void ImportExport::addWarningOnce(const QString& str)
+{
+	if (std::find(warnings_.begin(), warnings_.end(), str) == warnings_.end())
+		warnings_.emplace_back(str);
+}
+
+
 // ### Importer ###
 
 Importer::~Importer() = default;

src/fileformats/file_import_export.h

@@ -1,6 +1,6 @@
 /*
  *    Copyright 2012, 2013 Pete Curtis
- *    Copyright 2018 Kai Pastor
+ *    Copyright 2018, 2024 Kai Pastor
  *
  *    This file is part of OpenOrienteering.
  *
@@ -112,6 +112,13 @@ class ImportExport
 	 */
 	void addWarning(const QString& str) { warnings_.emplace_back(str); }
 
+	/**
+	 * Adds a string to the current list of warnings if not yet in the list.
+	 * 
+	 * The provided message should be translated.
+	 */
+	void addWarningOnce(const QString& str);
+	
 	/**
 	 * Returns the current list of warnings collected by this object.
 	 */