Eeschema: fix broken symbol library links after sheet edit.

Refresh the currently edit sheet screen symbol links when the sheet file
name is changed.

This fix was better than the previous fix as it was the same diff between
the master and 5.1 branches.

https://bugs.launchpad.net/kicad/+bug/1830315

Fixes lp:1830315

(cherry picked from commit 89ada624d3d3b28ad5ee1477b353501d46dae3a2)

eeschema/sheet.cpp

@@ -252,6 +252,11 @@ bool SCH_EDIT_FRAME::EditSheet( SCH_SHEET* aSheet, SCH_SHEET_PATH* aHierarchy,
 
             return false;
         }
+
+        SCH_SCREEN* screen = aSheet->GetScreen();
+
+        if( screen )
+            screen->UpdateSymbolLinks( true );
     }
 
     aSheet->SetFileNameSize( dlg.GetFileNameTextSize() );