[CF 5639] v2 - assert that wrapper_handler()'s argument is within expected range

This branch was automatically generated by a robot using patches from an
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https://commitfest.postgresql.org/patch/5639

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Patch(es): https://www.postgresql.org/message-id/Z8tZV4zv4uoAFHNa@nathan
Author(s): Nathan Bossart

Author: Commitfest Bot

src/port/pqsignal.c

@@ -87,6 +87,9 @@ wrapper_handler(SIGNAL_ARGS)
 {
 	int			save_errno = errno;
 
+	Assert(postgres_signal_arg > 0);
+	Assert(postgres_signal_arg < PG_NSIG);
+
 #ifndef FRONTEND
 
 	/*
@@ -123,6 +126,7 @@ pqsignal(int signo, pqsigfunc func)
 	struct sigaction act;
 #endif
 
+	Assert(signo > 0);
 	Assert(signo < PG_NSIG);
 
 	if (func != SIG_IGN && func != SIG_DFL)