Segfault when highlighting/selecting cols/rows near the bottom in fullscreen SDL

[toomykins]

In trying to get PDCurses full-screen, i noticed this little error where the program would give off a segmentation fault core dump when i tried to select/highlight near the bottom with my mouse.
According to gdb the error comes from _highlight() in getch.c, and i suspect it's this bit going out of bounds
curscr->_y[j][i] ^= A_REVERSE;
Probably has something to do with the way SDL handles resize_term aka PDC_resize_screen.
Happens in both versions of SDL, tested on Linux Ubuntu 20.04
quick way i tested it was by rightclicking the rain demo's title bar and selecting fullscreen on XFCE4, then trying to mouse-cursor-select down to the bottom-right.

[Bill-Gray]

I've a two-monitor system. Both are 1920x1080, but one is in portrait mode.

I could replicate this crash on the landscape-mode screen, where the bottom line is 'partial' (the screen height is not an even multiple of the font height). I couldn't replicate it on the portrait-mode screen, where there is no partial bottom line. It affected rain and other demos.

The problem arises because SDLn gets a mouse event in the partial line and (in this case) we're highlighting, say, the 42nd line on a screen with only 41 "full" lines. We just need to ignore mouse events in the partial line area (or in partial columns, should such arise).

I never noticed this before because for non-fullscreen windows, there are no partial rows or columns.

The patch I've made for PDCursesMod will need some minor modifications for PDCurses, but not much. Haven't checked yet to see if this affects X11 or (for PDCursesMod) WinGUI or DOSVGA.