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)

src/mouse.c

@@ -3099,7 +3099,7 @@ f_getmousepos(typval_T *argvars UNUSED, typval_T *rettv)
 	    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))
+		(void)mouse_comp_pos(wp, &row, &col, &lnum, NULL);
 		col = vcol2col(wp, lnum, col);
 		column = col + 1;
 	    }

src/testdir/test_functions.vim

@@ -2783,6 +2783,29 @@ func Test_getmousepos()
         \ line: 1,
         \ column: 8,
         \ }, getmousepos())
+
+  " If the mouse is positioned past the last buffer line, "line" and "column"
+  " should act like it's positioned on the last buffer line.
+  call test_setmouse(2, 25)
+  call assert_equal(#{
+        \ screenrow: 2,
+        \ screencol: 25,
+        \ winid: win_getid(),
+        \ winrow: 2,
+        \ wincol: 25,
+        \ line: 1,
+        \ column: 4,
+        \ }, getmousepos())
+  call test_setmouse(2, 50)
+  call assert_equal(#{
+        \ screenrow: 2,
+        \ screencol: 50,
+        \ winid: win_getid(),
+        \ winrow: 2,
+        \ wincol: 50,
+        \ line: 1,
+        \ column: 8,
+        \ }, getmousepos())
   bwipe!
 endfunc
 

src/version.c

@@ -750,6 +750,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    4568,
 /**/
     4567,
 /**/