fixed 'docker-entrypoint.sh: line 17: [: : integer expression expected'

Author: handcode

php-7.0/image-files/usr/local/bin/docker-entrypoint.sh

@@ -14,7 +14,7 @@ if [ -x "usermod" ] ; then
 fi
 
 # Enable xdebug by ENV variable
-if [ 0 -ne "${PHP_ENABLE_XDEBUG}" ] ; then
+if [ 0 -ne "${PHP_ENABLE_XDEBUG:-0}" ] ; then
     docker-php-ext-enable xdebug
     echo "Enabled xdebug"
 fi