patch 8.2.5093: error message for unknown command may have the command twice

Problem:    Error message for unknown command may mention the command twice.
            (Malcolm Rowe)
Solution:   Add the did_append_cmd flag. (closes #10570)
diff --git a/src/ex_docmd.c b/src/ex_docmd.c
index 23867d8..fed9330 100644
--- a/src/ex_docmd.c
+++ b/src/ex_docmd.c
@@ -1744,6 +1744,7 @@
     int		did_set_expr_line = FALSE;
 #endif
     int		sourcing = flags & DOCMD_VERBOSE;
+    int		did_append_cmd = FALSE;
 
     CLEAR_FIELD(ea);
     ea.line1 = 1;
@@ -2019,6 +2020,7 @@
 		    append_command(after_modifier);
 		else
 		    append_command(*cmdlinep);
+		did_append_cmd = TRUE;
 	    }
 	    errormsg = (char *)IObuff;
 	    did_emsg_syntax = TRUE;
@@ -2609,7 +2611,7 @@
 
     if (errormsg != NULL && *errormsg != NUL && !did_emsg)
     {
-	if (sourcing || !KeyTyped)
+	if ((sourcing || !KeyTyped) && !did_append_cmd)
 	{
 	    if (errormsg != (char *)IObuff)
 	    {