fixed enabled accounts check in onCreate

src/main/java/eu/siacs/conversations/services/XmppConnectionService.java

@@ -2538,6 +2538,9 @@ public class XmppConnectionService extends Service {
 	}
 
 	private boolean hasEnabledAccounts() {
+	    if (this.accounts == null) {
+	        return false;
+	    }
 	    for (Account account : this.accounts) {
 	        if (account.isEnabled()) {
 	            return true;