patch 9.0.1442: mapset() does not restore non-script context

Problem:    mapset() does not restore non-script context.
Solution:   Also accept negative sid. (closes #12132)

src/map.c

@@ -227,7 +227,7 @@ map_add(
 	int	    is_abbr,
 #ifdef FEAT_EVAL
 	int	    expr,
-	scid_T	    sid,	    // -1 to use current_sctx
+	scid_T	    sid,	    // 0 to use current_sctx
 	int	    scriptversion,
 	linenr_T    lnum,
 #endif
@@ -266,7 +266,7 @@ map_add(
     mp->m_simplified = simplified;
 #ifdef FEAT_EVAL
     mp->m_expr = expr;
-    if (sid > 0)
+    if (sid != 0)
     {
 	mp->m_script_ctx.sc_sid = sid;
 	mp->m_script_ctx.sc_lnum = lnum;
@@ -924,7 +924,7 @@ do_map(
 	if (map_add(map_table, abbr_table, keys, rhs, orig_rhs,
 		    noremap, nowait, silent, mode, abbrev,
 #ifdef FEAT_EVAL
-		    expr, /* sid */ -1, /* scriptversion */ 0, /* lnum */ 0,
+		    expr, /* sid */ 0, /* scriptversion */ 0, /* lnum */ 0,
 #endif
 		    keyround1_simplified) == FAIL)
 	{

src/testdir/test_map_functions.vim

@@ -1,6 +1,8 @@
 " Tests for maparg(), mapcheck(), mapset(), maplist()
 " Also test utf8 map with a 0x80 byte.
 
+source shared.vim
+
 func s:SID()
   return str2nr(matchstr(expand('<sfile>'), '<SNR>\zs\d\+\ze_SID$'))
 endfunc
@@ -490,7 +492,28 @@ func Test_map_restore()
   call Check_ctrlb_map(dsimp, 0)
 
   nunmap <C-B>
+endfunc
 
+" Test restoring the script context of a mapping
+func Test_map_restore_sid()
+  let after =<< trim [CODE]
+    call assert_equal("\tLast set from --cmd argument",
+          \ execute('verbose nmap ,n')->trim()->split("\n")[-1])
+    let d = maparg(',n', 'n', 0, 1)
+    nunmap ,n
+    call assert_equal('No mapping found',
+          \ execute('verbose nmap ,n')->trim()->split("\n")[-1])
+    call mapset('n', 0, d)
+    call assert_equal("\tLast set from --cmd argument",
+          \ execute('verbose nmap ,n')->trim()->split("\n")[-1])
+    call writefile(v:errors, 'Xresult')
+    qall!
+  [CODE]
+
+  if RunVim([], after, '--clean --cmd "nmap ,n <Nop>"')
+    call assert_equal([], readfile('Xresult'))
+  endif
+  call delete('Xresult')
 endfunc
 
 def Test_maplist()

src/version.c

@@ -695,6 +695,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1442,
 /**/
     1441,
 /**/