patch 8.2.1283: Vim9: error for misplaced -> lacks argument

Problem:    Vim9: error for misplaced -> lacks argument.
Solution:   Use the pointer before it was advanced.
diff --git a/src/testdir/test_vim9_expr.vim b/src/testdir/test_vim9_expr.vim
index b0a83f4..d7072f3 100644
--- a/src/testdir/test_vim9_expr.vim
+++ b/src/testdir/test_vim9_expr.vim
@@ -1532,7 +1532,7 @@
 
   call CheckDefFailure(["let x = ''", "let y = x.memb"], 'E715:')
 
-  call CheckDefFailure(["'yes'->", "Echo()"], 'E488:')
+  call CheckDefFailure(["'yes'->", "Echo()"], 'E488: Trailing characters: ->')
 
   call CheckDefExecFailure(["[1, 2->len()"], 'E697:')
   call CheckDefExecFailure(["#{a: 1->len()"], 'E488:')
diff --git a/src/version.c b/src/version.c
index 4ef3051..ab41071 100644
--- a/src/version.c
+++ b/src/version.c
@@ -755,6 +755,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1283,
+/**/
     1282,
 /**/
     1281,
diff --git a/src/vim9compile.c b/src/vim9compile.c
index 0fe0b16..3be8733 100644
--- a/src/vim9compile.c
+++ b/src/vim9compile.c
@@ -3761,6 +3761,8 @@
 	}
 	else if (*p == '-' && p[1] == '>')
 	{
+	    char_u *pstart = p;
+
 	    if (generate_ppconst(cctx, ppconst) == FAIL)
 		return FAIL;
 
@@ -3786,7 +3788,7 @@
 		p = *arg;
 		if (!eval_isnamec1(*p))
 		{
-		    semsg(_(e_trailing_arg), p);
+		    semsg(_(e_trailing_arg), pstart);
 		    return FAIL;
 		}
 		if (ASCII_ISALPHA(*p) && p[1] == ':')