patch 9.0.0051: using CTRL-C wih :append may hang Vim

Problem:    Using CTRL-C wih :append may hang Vim.
Solution:   Reset got_int. (closes #10729, closes #10728)

src/ex_getln.c

@@ -1786,6 +1786,8 @@ getcmdline_int(
 				// that occurs while typing a command should
 				// cause the command not to be executed.
 
+	got_int = FALSE;	// avoid infinite Ctrl-C loop in Ex mode
+
 	// Trigger SafeState if nothing is pending.
 	may_trigger_safestate(xpc.xp_numfiles <= 0);