Fix #318326 - System Text Line missing in existing parts when added v…

…ia drag&drop to non-top staff

If a TEXTLINE is dropped in a ScoreView, set firstStaffOnly to true if the dropped textline is a System TextLine.

src/notation/internal/notationinteraction.cpp

@@ -763,9 +763,12 @@ bool NotationInteraction::drop(const QPointF& pos, Qt::KeyboardModifiers modifie
     startEdit();
     score()->addRefresh(m_dropData.ed.dropElement->canvasBoundingRect());
     switch (m_dropData.ed.dropElement->type()) {
+    case ElementType::TEXTLINE:
+        firstStaffOnly = m_dropData.ed.dropElement->systemFlag();
+    // fall-thru
     case ElementType::VOLTA:
         // voltas drop to first staff by default, or closest staff if Control is held
-        firstStaffOnly = !(m_dropData.ed.modifiers & Qt::ControlModifier);
+        firstStaffOnly = firstStaffOnly || !(m_dropData.ed.modifiers & Qt::ControlModifier);
     // fall-thru
     case ElementType::OTTAVA:
     case ElementType::TRILL:
@@ -774,7 +777,6 @@ bool NotationInteraction::drop(const QPointF& pos, Qt::KeyboardModifiers modifie
     case ElementType::VIBRATO:
     case ElementType::PALM_MUTE:
     case ElementType::HAIRPIN:
-    case ElementType::TEXTLINE:
     {
         Ms::Spanner* spanner = ptr::checked_cast<Ms::Spanner>(m_dropData.ed.dropElement);
         score()->cmdAddSpanner(spanner, pos, firstStaffOnly);