Fix scolling in modes that have extra rows

EGA 80x43 has an extra six pixels at the bottom that are not part
of the text area.  When scrolling the botmap buffer, be sure to not
update this area.

Also, fix some screen invalidation bits when setting pixels.

This should fix ticket 180.

src/conio/bitmap_con.c

@@ -1473,6 +1473,11 @@ bitmap_movetext_screen(int x, int y, int tox, int toy, int direction, int height
 	int step;
 	int32_t screeny;
 
+	int pheight = height * vstat.charheight;
+	int ptoy = (toy - 1) * vstat.charheight;
+	int py = (y - 1) * vstat.charheight;
+	int ptox = (tox - 1) * vstat.charwidth;
+	int px = (x - 1) * vstat.charwidth;
 	pthread_mutex_lock(&screenlock);
 	if (width == vstat.cols && (height > vstat.rows / 2) && toy == 1) {
 		screena.toprow += (y - toy) * vstat.charheight;
@@ -1486,6 +1491,7 @@ bitmap_movetext_screen(int x, int y, int tox, int toy, int direction, int height
 		if (screena.toprow < 0)
 			screena.toprow += screena.screenheight;
 
+		int yoff = toy - y;
 		height = vstat.rows - height;
 		toy = vstat.rows - (height - 1);
 		// Fill the bits with impossible data so they're redrawn
@@ -1494,22 +1500,34 @@ bitmap_movetext_screen(int x, int y, int tox, int toy, int direction, int height
 			memset(&bitmap_drawn[bdoff], 0x04, sizeof(*bitmap_drawn) * vstat.cols);
 			bdoff = vmem_next_row_offset(vstat.vmem, bdoff);
 		}
-		pthread_mutex_unlock(&screenlock);
-		return;
+		if (vstat.charheight * vstat.rows == screena.screenheight) {
+			pthread_mutex_unlock(&screenlock);
+			return;
+		}
+		// Move stuff below the bottom row of text back
+		pheight = screena.screenheight - (vstat.charheight * vstat.rows);
+		ptoy = screena.screenheight - pheight;
+		py = ptoy + (yoff * vstat.charheight);
+		if (py < 0)
+			py += screena.screenheight;
+		if (py >= screena.screenheight)
+			py -= screena.screenheight;
 	}
 
 	int maxpos = screena.screenwidth * screena.screenheight;
 	if (direction == -1) {
-		ssourcepos = ((y + height - 1)      * vstat.charheight - 1) * vstat.scrnwidth + (x -   1) * vstat.charwidth;
-		sdestoffset = ((((toy + height - 1) * vstat.charheight - 1) * vstat.scrnwidth + (tox - 1) * vstat.charwidth) - ssourcepos);
+		ssourcepos =   (py   + pheight - 1) * vstat.scrnwidth + px;
+		sdestoffset = ((ptoy + pheight - 1) * vstat.scrnwidth + ptox) - ssourcepos;
 	}
 	else {
-		ssourcepos=(y - 1)     * vstat.scrnwidth * vstat.charheight + (x - 1)  * vstat.charwidth;
-		sdestoffset=(((toy - 1) * vstat.scrnwidth * vstat.charheight + (tox - 1) * vstat.charwidth) - ssourcepos);
+		ssourcepos =   py   * vstat.scrnwidth + px;
+		sdestoffset = (ptoy * vstat.scrnwidth + ptox) - ssourcepos;
 	}
 	ssourcepos += screena.toprow * screena.screenwidth;
+	if (ssourcepos >= maxpos)
+		ssourcepos -= maxpos;
 	step = direction * vstat.scrnwidth;
-	for(screeny=0; screeny < height*vstat.charheight; screeny++) {
+	for(screeny=0; screeny < pheight; screeny++) {
 		if (ssourcepos >= maxpos)
 			ssourcepos -= maxpos;
 		if (ssourcepos < 0)
@@ -1830,11 +1848,11 @@ int bitmap_setpixels(uint32_t sx, uint32_t sy, uint32_t ex, uint32_t ey, uint32_
 	bool yupdated = false;
 	int off;
 	for (y = sy; y <= ey; y++) {
+		charx = charsx;
 		pos = pixels->width*(y-sy+y_off)+x_off;
 		if (!yupdated) {
 			off = vmem_cell_offset(vstat.vmem, charx, chary);
 		}
-		charx = charsx;
 		if (mask == NULL) {
 			for (x = sx; x <= ex; x++) {
 				if (!yupdated) {
@@ -1930,6 +1948,7 @@ int bitmap_setpixels(uint32_t sx, uint32_t sy, uint32_t ex, uint32_t ey, uint32_
 		}
 		cpy++;
 		if (cpy >= vstat.charheight) {
+			chary++;
 			cpy = 0;
 			yupdated = false;
 			xupdated = false;