Make TextSelectionSizer a bit easier to understand standalone

Nothing really changes because it's only used in one place and that
place called getRegion so there's no leak but looking at the class
standalone one could think that one would get a leak if getRegion was
not called.
7 jobs for TextSelectionSizer in 3 minutes and 48 seconds (queued for 1 second)
Status Job ID Name Coverage
  Build
passed #7462978
build

00:03:36

passed #7462983
build_android

00:00:39

passed #7462979
build_clang_libcpp

00:03:45

passed #7462982
build_clazy

00:03:21

passed #7462981
build_mingw64_fedora

00:01:54

passed #7462980
build_ubuntu_16_04

00:01:48

passed #7462977
clang_format

00:01:32