patch 8.2.4427: getchar() may return modifiers if no character is ava…

…ilable

Problem:    getchar() may return modifiers if no character is available.
Solution:   Do not process modifiers when there is no character. (closes #9806)

src/getchar.c

@@ -2103,7 +2103,7 @@ getchar_common(typval_T *argvars, typval_T *rettv)
     set_vim_var_nr(VV_MOUSE_COL, 0);
 
     rettv->vval.v_number = n;
-    if (IS_SPECIAL(n) || mod_mask != 0)
+    if (n != 0 && (IS_SPECIAL(n) || mod_mask != 0))
     {
 	char_u		temp[10];   // modifier: 3, mbyte-char: 6, NUL: 1
 	int		i = 0;

src/testdir/test_functions.vim

@@ -1818,6 +1818,10 @@ func Test_getchar()
   call assert_equal('', getcharstr(0))
   call assert_equal('', getcharstr(1))
 
+  call feedkeys("\<M-F2>", '')
+  call assert_equal("\<M-F2>", getchar(0))
+  call assert_equal(0, getchar(0))
+
   call setline(1, 'xxxx')
   call test_setmouse(1, 3)
   let v:mouse_win = 9

src/version.c

@@ -750,6 +750,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    4427,
 /**/
     4426,
 /**/