patch 9.0.0715: wrong argument for append() gives two error messages

Problem:    Wrong argument for append() gives two error messages.
Solution:   When getting an error for a number argument don't try using it as
            a string. (closes vim#11335)

src/testdir/test_functions.vim

@@ -950,6 +950,8 @@ func Test_append()
 
   " Using $ instead of '$' must give an error
   call assert_fails("call append($, 'foobar')", 'E116:')
+
+  call assert_fails("call append({}, '')", ['E728:', 'E728:'])
 endfunc
 
 " Test for setline()

src/typval.c

@@ -2509,10 +2509,12 @@ eval_env_var(char_u **arg, typval_T *rettv, int evaluate)
 tv_get_lnum(typval_T *argvars)
 {
     linenr_T	lnum = -1;
+    int		did_emsg_before = did_emsg;
 
     if (argvars[0].v_type != VAR_STRING || !in_vim9script())
 	lnum = (linenr_T)tv_get_number_chk(&argvars[0], NULL);
-    if (lnum <= 0 && argvars[0].v_type != VAR_NUMBER)
+    if (lnum <= 0 && did_emsg_before == did_emsg
+					    && argvars[0].v_type != VAR_NUMBER)
     {
 	int	fnum;
 	pos_T	*fp;

src/version.c

@@ -699,6 +699,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    715,
 /**/
     714,
 /**/