patch 8.2.1848: crash when passing a NULL string or list to popup_settext()

Problem:    Crashyyyyy passing a NULL string or list to popup_settext().
Solution:   Check for NULL pointers. (closes #7132)

src/popupwin.c

@@ -1595,14 +1595,16 @@ popup_set_buffer_text(buf_T *buf, typval_T text)
     // Add text to the buffer.
     if (text.v_type == VAR_STRING)
     {
+	char_u *s = text.vval.v_string;
+
 	// just a string
-	ml_append_buf(buf, 0, text.vval.v_string, (colnr_T)0, TRUE);
+	ml_append_buf(buf, 0, s == NULL ? (char_u *)"" : s, (colnr_T)0, TRUE);
     }
     else
     {
 	list_T *l = text.vval.v_list;
 
-	if (l->lv_len > 0)
+	if (l != NULL && l->lv_len > 0)
 	{
 	    if (l->lv_first->li_tv.v_type == VAR_STRING)
 		// list of strings

src/testdir/test_popupwin.vim

@@ -2363,6 +2363,16 @@ func Test_popup_settext_getline()
   call popup_close(id)
 endfunc
 
+func Test_popup_settext_null()
+  let id = popup_create('', #{ tabpage: 0 })
+  call popup_settext(id, test_null_list())
+  call popup_close(id)
+
+  let id = popup_create('', #{ tabpage: 0 })
+  call popup_settext(id, test_null_string())
+  call popup_close(id)
+endfunc
+
 func Test_popup_hidden()
   new
 

src/version.c

@@ -750,6 +750,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1848,
 /**/
     1847,
 /**/