Linux: Fix storing previously synchronized clipboard

Fixes #2630

Author: hluk

src/app/clipboardmonitor.cpp

@@ -22,6 +22,17 @@ namespace {
 
 bool hasSameData(const QVariantMap &data, const QVariantMap &lastData)
 {
+    // Detect change also in case the data is unchanged but previously copied
+    // by CopyQ and now externally. This solves storing a copied text which was
+    // previously synchronized from selection to clipboard via CopyQ.
+    if (
+            !lastData.value(mimeOwner).toByteArray().isEmpty()
+            && data.value(mimeOwner).toByteArray().isEmpty()
+       )
+    {
+        return false;
+    }
+
     for (auto it = lastData.constBegin(); it != lastData.constEnd(); ++it) {
         const auto &format = it.key();
         if ( !format.startsWith(COPYQ_MIME_PREFIX)