Fix FormulaCreator.dequote for symbol names have a length < 2

Author: daniel-raffler

src/org/sosy_lab/java_smt/basicimpl/FormulaCreator.java

@@ -785,7 +785,7 @@ public Object convertValue(
   /** Variable names (symbols) can be wrapped with "|". This function removes those chars. */
   protected static String dequote(String s) {
     int l = s.length();
-    if (s.charAt(0) == '|' && s.charAt(l - 1) == '|') {
+    if (l >= 2 && s.charAt(0) == '|' && s.charAt(l - 1) == '|') {
       return s.substring(1, l - 1);
     }
     return s;