QComposeInputContext: reduce composeBuffer to QT_KEYSEQUENCE_MAX_LEN

The extra length has been used for a sentinel null value.
By checking the index before indexing into the array, that
extra element can be dropped.

Change-Id: I0b309420d8d89f75e2381a8065c8e68a1a33427c
Reviewed-by: Marc Mutz <marc.mutz@kdab.com>
Reviewed-by: Lars Knoll <lars.knoll@theqtcompany.com>

src/plugins/platforminputcontexts/compose/qcomposeplatforminputcontext.cpp

@@ -111,7 +111,7 @@ bool QComposeInputContext::filterEvent(const QEvent *event)
     keysym = keyEvent->nativeVirtualKey();
 
     int nCompose = 0;
-    while (m_composeBuffer[nCompose] != 0 && nCompose < QT_KEYSEQUENCE_MAX_LEN)
+    while (nCompose < QT_KEYSEQUENCE_MAX_LEN && m_composeBuffer[nCompose] != 0)
         nCompose++;
 
     if (nCompose == QT_KEYSEQUENCE_MAX_LEN) {

src/plugins/platforminputcontexts/compose/qcomposeplatforminputcontext.h

@@ -68,7 +68,7 @@ protected:
 private:
     QObject *m_focusObject;
     QVector<QComposeTableElement> m_composeTable;
-    uint m_composeBuffer[QT_KEYSEQUENCE_MAX_LEN + 1];
+    uint m_composeBuffer[QT_KEYSEQUENCE_MAX_LEN];
     TableGenerator::TableState m_tableState;
     bool m_compositionTableInitialized;
 };