mainly by using for range loops
+ by using empty() instead of comparing begin and iterator
or use size to test that a container has at least 2 elements

Change-Id: I81f168d8c36a8b4195fbb0c1aee4983dab25d22c
Reviewed-on: https://gerrit.libreoffice.org/50705Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Julien Nabet <serval2412@yahoo.fr>