patch 8.1.1611: bufadd() reuses existing buffer without a name

Problem:    Bufadd() reuses existing buffer without a name.
Solution:   When the name is empty always create a new buffer.

src/evalfunc.c

@@ -1929,7 +1929,9 @@ find_buffer(typval_T *avar)
     static void
 f_bufadd(typval_T *argvars, typval_T *rettv)
 {
-    rettv->vval.v_number = buflist_add(tv_get_string(&argvars[0]), 0);
+    char_u *name = tv_get_string(&argvars[0]);
+
+    rettv->vval.v_number = buflist_add(*name == NUL ? NULL : name, 0);
 }
 
 /*

src/testdir/test_functions.vim

@@ -1539,6 +1539,20 @@ func Test_bufadd_bufload()
   call assert_equal(['some', 'text'], getbufline(buf, 1, '$'))
   call assert_equal(curbuf, bufnr(''))
 
+  let buf1 = bufadd('')
+  let buf2 = bufadd('')
+  call assert_notequal(0, buf1)
+  call assert_notequal(0, buf2)
+  call assert_notequal(buf1, buf2)
+  call assert_equal(1, bufexists(buf1))
+  call assert_equal(1, bufexists(buf2))
+  call assert_equal(0, bufloaded(buf1))
+  exe 'bwipe ' .. buf1
+  call assert_equal(0, bufexists(buf1))
+  call assert_equal(1, bufexists(buf2))
+  exe 'bwipe ' .. buf2
+  call assert_equal(0, bufexists(buf2))
+
   bwipe someName
   bwipe otherName
   call assert_equal(0, bufexists('someName'))

src/version.c

@@ -777,6 +777,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1611,
 /**/
     1610,
 /**/