replaced exception with warning if maximum number of colors is reached; fixes T250

src/gui_qt/graphs/graphwindow.py

@@ -520,14 +520,16 @@ class QGraphWindow(QtWidgets.QGraphicsView, Ui_GraphWindow):
                 elif other_item in self.graphic.items():
                     self.legend.addItem(other_item, convert(other_item.opts.get('name', ''), old='tex', new='html'))
 
-    def export_dialog(self):
+    def export_dialog(self, path=None):
         filters = 'All files (*.*);;AGR (*.agr);;SVG (*.svg);;PDF (*.pdf)'
         for imgformat in QtGui.QImageWriter.supportedImageFormats():
             str_format = imgformat.data().decode('utf-8')
             filters += ';;' + str_format.upper() + ' (*.' + str_format + ')'
 
+        if path is None:
+            path = ''
         outfile = None
-        f = FileDialog(caption='Export graphic', filters=filters)
+        f = FileDialog(caption='Export graphic', directory=str(path), filter=filters)
         mode = f.exec()
         if mode == QtWidgets.QDialog.Accepted:
             outfile = f.save_file()