Strings: fix random generator alphabet labels

alib2algo/src/string/generate/RandomStringFactory.cpp

@@ -40,7 +40,7 @@ string::LinearString < > RandomStringFactory::generateLinearString ( size_t size
 	std::vector < alphabet::Symbol > symbols;
-	for ( int i = 0; i < 26; i++ ) symbols.push_back ( alphabet::symbolFrom ( i + 'a' ) );
+	for ( int i = 0; i < 26; i++ ) symbols.push_back ( alphabet::symbolFrom ( ( char ) ( i + 'a' ) ) );
 	if ( randomizedAlphabet ) shuffle ( symbols.begin ( ), symbols.end ( ), std::random_devices::semirandom );