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 #11335)
diff --git a/src/typval.c b/src/typval.c
index a4fdb78..d6f6196 100644
--- a/src/typval.c
+++ b/src/typval.c
@@ -2509,10 +2509,12 @@
 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;