LogDlg: StatGraph: replace "fetch" with "calculate" to avoid confuse

Signed-off-by: Frank Li <lznuaa@gmail.com>
LogDlg: StatGraph: avoid call RedrawGraph twice on OnInitDialog

OnCbnSelchangeGraphcombo() will call RedrawGraph and need call redrawGraph again.
Otherwise, user how to cancel twice when log lines statistic view is default view

Signed-off-by: Frank Li <lznuaa@gmail.com>