Clear the exit code from 'find' in 'make depend'

Depending on what has been built so far, all .d files may not be
present and 'find' will exit with non-zero exit code.  This isn't a
bother for us but may break make, so clear the exit code with an added
'exit 0'.

Closes RT#4444
Reviewed-by: NRich Salz <rsalz@openssl.org>

Configurations/unix-Makefile.tmpl

@@ -260,7 +260,7 @@ clean: libclean
 # concatenate only if that is true.
 depend:
 	@: {- output_off() if $disabled{makedepend}; "" -}
-	@if [ -z "`find $(DEPS) -newer Makefile 2>/dev/null`" ]; then \
+	@if [ -z "`find $(DEPS) -newer Makefile 2>/dev/null; exit 0`" ]; then \
 	  ( sed -e '/^# DO NOT DELETE THIS LINE.*/,$$d' < Makefile; \
 	    echo '# DO NOT DELETE THIS LINE -- make depend depends on it.'; \
 	    echo; \