fix negative size when zooming out

Frontend/patient_manager/lib/pages/fullScreenFile.dart

@@ -206,10 +206,12 @@ class _FullScreenFileViewerState extends State<FullScreenFileViewer> {
                           startZoomLevel = pdfViewerController.zoomLevel;
                         });
                       } else {
+                        if (zoomOut < (width - 100)) {
                           setState(() {
                             zoomOut = zoomOut + 100;
                           });
                         }
+                      }
                     },
                     icon: Icon(
                       Icons.zoom_out,