Fix StackOverflow in variable parsing (#7809)

Author: sovdeeth

src/main/java/ch/njol/skript/variables/FlatFileStorage.java

@@ -530,8 +530,17 @@ static byte[] decode(String hex) {
 
 	/**
 	 * A regex pattern of a line in a CSV file.
+	 * <ul>
+	 * <li>{@code (?<=^|,)}: assert that the match is preceded by the start of the line or a comma</li>
+	 * <li>{@code (?:([^",]*)|"((?:[^"]+|"")*)")}: match either a quoted or unquoted value</li>
+	 * <ul>
+	 * 	<li>- {@code ([^",]*)}: match an unquoted value</li>
+	 * 	<li>- {@code "((?:[^"]+|"")*)"}: match a quoted value</li>
+	 * </ul>
+	 * <li>{@code (?:,|$)}: match either a comma or the end of the line</li>
+	 * </ul>
 	 */
-	private static final Pattern CSV_LINE_PATTERN = Pattern.compile("(?<=^|,)\\s*([^\",]*|\"([^\"]|\"\")*\")\\s*(,|$)");
+	private static final Pattern CSV_LINE_PATTERN = Pattern.compile("(?<=^|,)\\s*(?:([^\",]*)|\"((?:[^\"]+|\"\")*)\")\\s*(?:,|$)");
 
 	/**
 	 * Splits the given CSV line into its values.
@@ -550,14 +559,15 @@ static String[] splitCSV(String line) {
 
 		while (matcher.find()) {
 			if (lastEnd != matcher.start())
-				return null; // other stuff inbetween finds
-
-			String value = matcher.group(1);
-			if (value.startsWith("\""))
-				// Unescape value
-				result.add(value.substring(1, value.length() - 1).replace("\"\"", "\""));
-			else
-				result.add(value.trim());
+				return null; // other stuff in between finds
+
+			if (matcher.group(1) != null) {
+				// unquoted, leave as is
+				result.add(matcher.group(1).trim());
+			} else {
+				// quoted, remove quotes
+				result.add(matcher.group(2).replace("\"\"", "\""));
+			}
 
 			lastEnd = matcher.end();
 		}