Protect move tool from re-entrancy.

m_dragInProgress is usually sufficient, except when we haven't started
one yet.  In any case, conflating the two is probably a bad idea.

Fixes https://gitlab.com/kicad/code/kicad/issues/12936

(cherry picked from commit bc271a8d15)

eeschema/tools/sch_move_tool.cpp

@@ -47,6 +47,7 @@
 
 SCH_MOVE_TOOL::SCH_MOVE_TOOL() :
         EE_TOOL_BASE<SCH_EDIT_FRAME>( "eeschema.InteractiveMove" ),
+        m_inMoveTool( false ),
         m_moveInProgress( false ),
         m_isDrag( false ),
         m_moveOffset( 0, 0 )
@@ -126,6 +127,11 @@ int SCH_MOVE_TOOL::Main( const TOOL_EVENT& aEvent )
         return 0;
     }
 
+    if( m_inMoveTool )      // Must come after m_moveInProgress checks above...
+        return 0;
+
+    REENTRANCY_GUARD guard( &m_inMoveTool );
+
     // Be sure that there is at least one item that we can move. If there's no selection try
     // looking for the stuff under mouse cursor (i.e. Kicad old-style hover selection).
     EE_SELECTION& selection = m_selectionTool->RequestSelection( EE_COLLECTOR::MovableItems );

eeschema/tools/sch_move_tool.h

@@ -81,6 +81,9 @@ private:
     void setTransitions() override;
 
 private:
+    ///< Re-entrancy guard
+    bool                  m_inMoveTool;
+
     ///< Flag determining if anything is being dragged right now
     bool                  m_moveInProgress;
     bool                  m_isDrag;