[MDITAB] Fix handling of do_redraw flag.
[MDITAB] Fix handling of do_redraw flag.

The flag was handled only in function for painting a single tab.
Furthermore it had impact on WM_PRINTCLIENT and not just WM_PAINT.
Fixed by moving the test into mditab_proc().

mity/mctrl,mity/mctrl,mity/mctrl,mity/mctrl