process db file only if it exists after db configuration

debian/template/postinst

@@ -44,23 +44,26 @@ case "$1" in
     invoke-rc.d --force postgresql restart || true
     dbc_go minerva $@
 
-    . /etc/minerva/db.sh
+    # if there is a config file generated by db_config_common (on upgrade this file might not be generated)
+  	if [ -f /etc/minerva/db.sh ]
+      . /etc/minerva/db.sh
     
-    # when configuration was cancelled don't create config file
-  	if [ ! -z "$dbuser" ]
-  	then
-      if [ -z "$dbport" ]
-      then
-        dbport=5432
-      fi
+      # when configuration was cancelled don't create config file
+  	  if [ -z "$dbuser" ]
+  	  then
+        if [ -z "$dbport" ]
+        then
+          dbport=5432
+        fi
     
-      #create db configuration file 
-      echo "database.uri=jdbc:postgresql://$dbserver:$dbport/$dbname" > /etc/minerva/db.properties
-      echo "database.username=$dbuser" >> /etc/minerva/db.properties
-      echo "database.password=$dbpass" >> /etc/minerva/db.properties
+        #create db configuration file 
+        echo "database.uri=jdbc:postgresql://$dbserver:$dbport/$dbname" > /etc/minerva/db.properties
+        echo "database.username=$dbuser" >> /etc/minerva/db.properties
+        echo "database.password=$dbpass" >> /etc/minerva/db.properties
     
+      fi
+      rm /etc/minerva/db.sh
     fi
-    rm /etc/minerva/db.sh
 
     #we have to restart tomcat, because application was started on the old database and it might crash during deployment
     #for instance in the new war file there was init script that uses some new database features, but they are not