patch 8.2.4568: getmousepos() does not compute the column below the last line

Problem:    getmousepos() does not compute the column below the last line.
Solution:   Also compute the column when the mouse is below the last line.
            (Sean Dewar, closes #9946)
diff --git a/src/mouse.c b/src/mouse.c
index 25d6fa8..ffbe842 100644
--- a/src/mouse.c
+++ b/src/mouse.c
@@ -3099,8 +3099,8 @@
 	    col -= left_off;
 	    if (row >= 0 && row < wp->w_height && col >= 0 && col < wp->w_width)
 	    {
-		if (!mouse_comp_pos(wp, &row, &col, &lnum, NULL))
-		    col = vcol2col(wp, lnum, col);
+		(void)mouse_comp_pos(wp, &row, &col, &lnum, NULL);
+		col = vcol2col(wp, lnum, col);
 		column = col + 1;
 	    }
 	}