In CON showview, if drawing off-screen, clear the view with pal 0 and bail out.

This fixes the glitches/corruption whereever showview is used from
EVENT_DISPLAYROOMS while the scene is actually rendered to a tile instead of the
frame buffer, for example because we have a tilted view or "pixel doubling"
enabled.  Fixing it for real (i.e. so that the showview actually completes)
will require more effort.

git-svn-id: https://svn.eduke32.com/eduke32@2706 1a8010ca-5511-0410-912e-c29ae57300e0

polymer/eduke32/source/game.c

@@ -3743,6 +3743,8 @@ void G_DrawRooms(int32_t snum, int32_t smoothratio)
             break;
         }
 
+        // NOTE: might be rendering off-screen here, so CON commands that draw stuff
+        //  like showview must cope with that situation or bail out!
         if (apScriptGameEvent[EVENT_DISPLAYROOMS])
             VM_OnEvent(EVENT_DISPLAYROOMS, g_player[screenpeek].ps->i, screenpeek, -1, 0);
 

polymer/eduke32/source/gameexec.c

@@ -2342,6 +2342,12 @@ nullquote:
 
                 if (g_screenCapture) continue;
 
+                if (offscreenrendering)
+                {
+                    clearview(0);
+                    continue;
+                }
+
                 if (x1 > x2) swaplong(&x1,&x2);
                 if (y1 > y2) swaplong(&y1,&y2);