bashrc: fix unbound variable warning of SSH_CONNECTION

Author: xtexx

bashrc

@@ -100,7 +100,7 @@ _ssh_session() {
 	# Store error code.
 	err="$?"
 	# This if branch would overwrite the current error code.
-	if [[ x"$SSH_CONNECTION" != "x" ]]; then
+	if [[ x"${SSH_CONNECTION:-}" != "x" ]]; then
 		echo '(ssh)'
 	fi
 	# Load error code.