Use hash (not page no) to determine when we've found the current sheet.

Also enforces strict ordering in another page number sorter, although
this has nothing to do with the bug below.

Fixes https://gitlab.com/kicad/code/kicad/issues/12043

eeschema/sch_sheet_path.cpp

@@ -735,7 +735,14 @@ void SCH_SHEET_LIST::SortByPageNumbers( bool aUpdateVirtualPageNums )
     std::sort( begin(), end(),
         []( SCH_SHEET_PATH a, SCH_SHEET_PATH b ) -> bool
         {
-             return a.ComparePageNum( b ) < 0;
+            int retval = a.ComparePageNum( b );
+
+            if( retval < 0 )
+                return true;
+            else if( retval > 0 )
+                return false;
+            else /// Enforce strict ordering.  If the page numbers are the same, use UUIDs
+                return a.GetCurrentHash() < b.GetCurrentHash();
         } );
 
     if( aUpdateVirtualPageNums )

eeschema/tools/sch_editor_control.cpp

@@ -531,7 +531,7 @@ int SCH_EDITOR_CONTROL::FindNext( const TOOL_EVENT& aEvent )
         {
             if( afterSheet )
             {
-                if( afterSheet->GetPageNumber() == sheet->GetPageNumber() )
+                if( afterSheet->GetCurrentHash() == sheet->GetCurrentHash() )
                     afterSheet = nullptr;
 
                 continue;