kamctl: check if kamctlrc is readable

- related to GH #3594

(cherry picked from commit a3fd3b12ca9b1c3688255e9d645085947052bc6d)
(cherry picked from commit 259812f03ec26d49776050ca5eb657f2771ce8d5)

utils/kamctl/kamctl

@@ -39,13 +39,13 @@ if [ -n "$KAMCTLFULLPATH" ] ; then
 fi
 
 # check for rc file at standard locations
-if [ -f /etc/kamailio/kamctlrc ]; then
+if [ -f /etc/kamailio/kamctlrc -a -r /etc/kamailio/kamctlrc ]; then
 	. /etc/kamailio/kamctlrc
 fi
-if [ -f /usr/local/etc/kamailio/kamctlrc ]; then
+if [ -f /usr/local/etc/kamailio/kamctlrc -a -r /usr/local/etc/kamailio/kamctlrc ]; then
 	. /usr/local/etc/kamailio/kamctlrc
 fi
-if [ -f ~/.kamctlrc ]; then
+if [ -f ~/.kamctlrc -a -r ~/.kamctlrc ]; then
 	. ~/.kamctlrc
 fi