Fixed read bug in Excel files with a ministream bigger than 1024 (1024 is a casual number, any other could raise the bug).

git-svn-id: https://svn.code.sf.net/p/lazarus-ccr/svn@955 8e941d3f-bd1b-0410-a28a-d453659cc2b4

components/fpspreadsheet/uvirtuallayer_ole_helpers.pas

@@ -731,6 +731,7 @@ begin
       //Read it from MiniFAT
       AContext.MiniStream.Position:=AContext.Position;
       Result:=AContext.MiniStream.Read(ABuffer^,ASize);
+      AContext.Position:=AContext.MiniStream.Position;
       Exit;
     end;
   end;