patch 8.1.1279: cannot set 'spellang' to "sr@latin"

Problem:    Cannot set 'spellang' to "sr@latin". (Bojan Stipic)
Solution:   Allow using '@' in 'spellang'. (closes #4342)
diff --git a/src/option.c b/src/option.c
index 9583aa3..657c011 100644
--- a/src/option.c
+++ b/src/option.c
@@ -6057,7 +6057,7 @@
     int
 valid_spellang(char_u *val)
 {
-    return valid_name(val, ".-_,");
+    return valid_name(val, ".-_,@");
 }
 
 /*
diff --git a/src/testdir/gen_opt_test.vim b/src/testdir/gen_opt_test.vim
index bd3f80c..74c725f 100644
--- a/src/testdir/gen_opt_test.vim
+++ b/src/testdir/gen_opt_test.vim
@@ -125,6 +125,7 @@
       \ 'sessionoptions': [['', 'blank', 'help,options,slash'], ['xxx']],
       \ 'signcolumn': [['', 'auto', 'no'], ['xxx', 'no,yes']],
       \ 'spellfile': [['', 'file.en.add'], ['xxx', '/tmp/file']],
+      \ 'spelllang': [['', 'xxx', 'sr@latin'], ['not&lang', "that\\\rthere"]],
       \ 'spellsuggest': [['', 'best', 'double,33'], ['xxx']],
       \ 'switchbuf': [['', 'useopen', 'split,newtab'], ['xxx']],
       \ 'tagcase': [['smart', 'match'], ['', 'xxx', 'smart,match']],
diff --git a/src/version.c b/src/version.c
index 0b47695..8ab83c3 100644
--- a/src/version.c
+++ b/src/version.c
@@ -768,6 +768,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1279,
+/**/
     1278,
 /**/
     1277,