Prevent duplicate entries in passphrase wordlists

Replace a QVector for the wordlist with a QSet. This removes all duplicate entries in a given wordlist.
Thus, it hinders a malicious wordlist that has the proper length (>4000 entries) but with repetitions (effectively << 4000 entries) to be used and potentially create weaker passphrases than estimated.

Example:
List with 4000 items but only 64 unique words would lead to only 48 bit of Entropy instead of ~95 bit!

tests/TestCli.cpp

@@ -1088,7 +1088,7 @@ void TestCli::testDiceware()
     smallWordFile.close();
 
     execCmd(dicewareCmd, {"diceware", "-W", "11", "-w", smallWordFile.fileName()});
-    QCOMPARE(m_stderr->readLine(), QByteArray("The word list is too small (< 1000 items)\n"));
+    QCOMPARE(m_stderr->readLine(), QByteArray("Cannot generate valid passphrases because the wordlist is too short\n"));
 }
 
 void TestCli::testEdit()

tests/TestPassphraseGenerator.cpp

@@ -16,6 +16,7 @@
  */
 
 #include "TestPassphraseGenerator.h"
+#include "config-keepassx-tests.h"
 #include "core/PassphraseGenerator.h"
 #include "crypto/Crypto.h"
 
@@ -52,3 +53,18 @@ void TestPassphraseGenerator::testWordCase()
     QRegularExpression regex("^(?:[A-Z][a-z-]* )*[A-Z][a-z-]*$");
     QVERIFY2(regex.match(passphrase).hasMatch(), qPrintable(passphrase));
 }
+
+void TestPassphraseGenerator::testUniqueEntriesInWordlist()
+{
+    PassphraseGenerator generator;
+    // set the limit down, so we don;t have to do a very large file
+    generator.m_minimum_wordlist_length = 4;
+
+    // link to bad wordlist
+    QString path = QString(KEEPASSX_TEST_DATA_DIR).append("/wordlists/bad_wordlist_with_duplicate_entries.wordlist");
+
+    // setting will work, it creates the warning however, and isValid will fail
+    generator.setWordList(path);
+    // so this fails
+    QVERIFY(!generator.isValid());
+}

tests/TestPassphraseGenerator.h

@@ -27,6 +27,7 @@ class TestPassphraseGenerator : public QObject
 private slots:
     void initTestCase();
     void testWordCase();
+    void testUniqueEntriesInWordlist();
 };
 
 #endif // KEEPASSXC_TESTPASSPHRASEGENERATOR_H

tests/data/wordlists/bad_wordlist_with_duplicate_entries.wordlist

@@ -0,0 +1,4 @@
+abacus
+abdomen
+abdominal
+abdominal